Web standards circles agree that "browser sniffing" as opposed to "feature detection" is kind of evil. (See http://modernizr.com for one way to do it right.) This, however, is a very special case, where the whole point is showing what ones specific browser can do.
Generally, the user's browser is irrelevant to the point of a website, and supporting as many browsers as possible is best.
In this case, the user’s browser matters most, as no other browser currently has 100% feature parity with Safari features used in these demos.
That's a good point. And I can understand that Apple, esp. if they are targeting creative / ad people, are probably aiming for a completely professional look (v. Flash, etc.). Until the other browsers catch up, I suppose they have every justification for doing what they're doing. One could argue, that they don't want browsers that aren't fully conforming which might give a bad impression of the viability of this post-Flash world.
On the other hand, browser sniffing, as you mention, is a slippery slope. Maybe all they might do is acknowledge that until other browsers have fully implemented 3D CSS, etc., they are only recommending Safari.
ETA: Never mind, I went back and read the page:
Not all browsers offer this support. But soon other modern browsers will take advantage of these same web standards — and the amazing things they enable web designers to do.
Web standards circles agree that "browser sniffing" as opposed to "feature detection" is kind of evil. (See http://modernizr.com for one way to do it right.) This, however, is a very special case, where the whole point is showing what ones specific browser can do.
Generally, the user's browser is irrelevant to the point of a website, and supporting as many browsers as possible is best.
In this case, the user’s browser matters most, as no other browser currently has 100% feature parity with Safari features used in these demos.