Apple is at the forefront of standards adoptions, Safari's got some stuff that other browsers don't, and they want to show it off! What on earth is wrong with this? Firefox has better standards support? So what? Are we claiming Apple has a moral imperative to create demos of Firefox-only standards support?! Or, is it the even crazier claim that only the "best" product is allowed to promote itself? If you're selling Porsches and you say they're fast, is this offensive because Ferraris are faster? Good God.
I've also never before seen anyone so self-righteous about the use of the term html5; there's nothing about Apple's page which deserves special enmity for its "misuse" of this ambiguous term. In fact, I'm pretty sure in the future we'll see plenty of articles talking about html5, just as we have in the past, e.g., scribd converting from flash.
If you can't see how a company might find value in illustrating how quickly it implements emerging standards, I suggest you aren't thinking about it very hard. This page isn't about why web standards are important for cross-platform compatibility. Criticizing it for not demonstrating something which is not is purpose is awfully silly.
The outrage stirred up by the last couple of posts on this subject strikes me as follow-on to other perceived "evils" by Apple, and seems to be heavily biased rather than treating this issue on its own ethically distinct terms. But then, that's what people do.