Web developers behind the sites on Apple’s approved list of iPad-ready online destinations have confronted an issue that the device-maker is forcing to the fore: are official World Wide Web Consortium standard languages sufficient tools to deliver cutting edge functionality, or do plug-ins lead the way in design innovation?

Soon after Apple unveiled the iPad in January, one point quickly became clear for Web developers: Just as with the iPhone, the device would not support Adobe Flash, or any other Web plug-in.

Instead, if Web developers wanted all the dynamic content on their pages such as videos and animations to appear correctly on Apple’s new device, they had to create it using only the next generation markup language for the Web, HTML5, and related open standards.

At first glance, it appears like a logical move to stick with open standards, rather than technology largely controlled by a single company.

“A lot of the things that Flash has traditionally been used for, were Flash’s domain, because there weren’t any credible open standards available. Now there are,” said Bruce Lawson, a vocal HTML5 advocate who also works on the Opera Software as a developer relations (for this interview, he stressed that his opinions were his own, and not those of Opera).

But a casual search on Google reveals that there are at least 74 million web pages that use the Shockwave Flash (SWF) format. It is a tall order to ask all of them to change for a single company’s line of products, even if Apple sold more than 500,000 of these devices last weekend.

Observers also note that the developer tools for HTML5 aren’t as advanced as those for Flash, and the standard is not finished yet, which could lead to more work for developers down the road to readjust pages to meet the finalized standard.

And by eschewing the Web’s plug-in model, the iPad may potentially miss out on cutting edge features enjoyed elsewhere on the Web.

For photo-sharing site Flickr, the chief feature on the site that needed to be addressed was video, which the company has been gradually introducing into its service.

“It was not a huge effort,” said Flickr Project Manager Markus Spiering, though quickly adding the site’s developers were already familiar with the standards that Apple was requiring for the device.

“We were using Flash for our video content, but the iPad doesn’t support Flash,” Spiering said. “The iPad has a built-in HTML5 video player, which we could leverage.”

The Web development team were already testing HTML5, and had already borrowed some of the work it did for the Apple TV, which worked well in the iPad format.

“It was a couple of days of testing and then we enabled it,” Spiering said.

Now, when an iPad user visits the Flickr site, the site’s servers determine the visitor is using that device and switches from sending the video to a Flash player to sending it to Apple’s HTML5 video player.

Spiering said that to offer video for all Flickr visitors using HTML5 would be a larger challenge, because additional controls — such as full screen capability — would need to be added to bring the browsers up to feature parity with the iPad.

Apple itself has released guidelines on how to prepare Web pages for the iPad. In a nutshell: All the capabilities you seek can be found by using Javascript, Cascading Styles Sheets (CSS) and a set of still-evolving standards loosely associated with the World Wide Web Consortium’s HTML5. What could not be used are plug-ins of any sort, including Adobe Flash.

Adobe has been, understandably, defensive over Apple’s stance, and playing up Flash’s use on other portable devices, as a way to deflect attention away from Apple’s decision.

However, Dave McAllister, Director of Open Source and Standards (OSS) at Adobe Systems suggests that Apple itself may be putting the iPad at a disadvantage by not including plug-ins.

“From our viewpoint, it’s not just the lack of Flash, it’s the lack of being able to use plug-ins that are not owned, controlled and approved, that is an issue,” McAllister said.

McAllister noted that innovation with the Web format has historically taken place not with the standards themselves, but rather plug-ins. Standards take years to ratify and tend to center around technology that has been so widely replicated, it has in effect been commoditized.

“Standards don’t lead innovation. To innovate means to build on or out from the existing platform,” McAllister said. “You don’t want to have to wait for the consistent commodity approach to catch back up to the innovation. You want innovation to happen, and [standardize] the best from it.”

It’s been the plug-in model that introduces new functionality to the Web, he argued. Think of Sun Microsystems’ Java plug-in, for instance, which introduced rich graphical functionality for the Web in the mid-1990s. By eschewing plug-ins, the iPad could potentially lose out on some of the cutting edge features enjoyed on other Web browsers.

Another issue that McAllister notes is that Web development shops will have to come up with two versions of their sites, ones that run Flash and ones that don’t. “Most of these [shops] already have Flash as part of their workflow, so now they are adding a second part of the workflow,” McAllister said.

For its part, HTML5 is starting to prove itself to be a very capable markup language, able, in theory, to replicate much if not all that Flash could offer. HTML5 and associated standards such as CSS and Scalable Vector Graphics (SVG), will be an “open platform for rich Web applications,” said Philippe Le Hégaret, who is the W3C’s interaction domain leader overseeing graphics, HTML, and video, in an e-mail.

Last week, Google engineers posted a version of Quake II that they ported to HTML5, using Javascript. Elsewhere in Google, a beta version of YouTube has been created that uses HTML5.

HTML5 and its related standards can cover a lot of Flash functionality, Lawson said. Simple animations can be recreated in CSS. More complex animations can be done with the HTML5 canvas tag in conjunction with Javascript.

But unlike Flash, HTML5 doesn’t yet have a lot of production-ready integrated developer environments. “Flash has very good authoring tools,” Lawson said. As McAllister noted, Dreamweaver and FlashBuilder are already incorporated into the day-to-day operations of many Web development shops.

In contrast, the tools for HTML5 and related technologies are still being developed. Worse yet, many are aimed more at the programmer than the run-of-the-mill Web designer. As one media company told the Valleywag industry gossip site, “Guess what, we don’t have a bunch of code junkies in our newsroom.” (Though Adobe itself seems to be in the early stages of incorporating the HTML5 standards into its own production tools, if this prototype of Dreamweaver that converts artwork into HTML5’s Canvas tag is any indication).

Another potential problem: The HTML5 standard has not actually been finalized yet.

“The HTML5 standard is still a work in progress,” Le Hégaret admitted. The problem is that until it is finalized, HTML5 may change. And if it does, all the pages affected by the changes will have to be revamped.

One bit of unfinished business is the HTML5 video tag. HTML5 allows pages to run video directly within the browser window, without a plug-in. The problem is, the browser makers are split over which video codec to use.

Google Chrome and Apple Safari natively support the high-definition H.264 MP4 format for this task. Neither Opera nor Firefox support this codec, due to concerns over licensing fees. Opera and Firefox, on the other hand, use open-source codec Ogg Theora, which Apple and Google have been reluctant to support, citing performance concerns. Microsoft hasn’t committed to either.

Overall, however, HTML5 may be closer to the finish line than its critics suggest. Lawson does not think that the W3C will make dramatic changes to the HTML5. “It seems to me that the main work on inventing new features is pretty much over,” he said. “It is possible that one or two features might get dropped because they are not being supported by any browsers, but the features that will be dropped are by definition ones not being widely used.”

For the foreseeable future, anyway, Web developers interested in tweaking their sites for the iPad, but also using continuing to use Flash, may have no choice but to build, as Flickr did, hooks specific for the iPad. And Flash itself, despite Steve Jobs’ wishes, is not going anywhere soon.

“I don’t think HTML5 will kill Flash in anything but the very long term. There is so much Flash content out there that will need to be supported,” Lawson said.