> The demos below show how Apple’s Safari web browser supports the capabilities of web standards such as HTML5, CSS3, and JavaScript.
Gruber’s point is this: if Opera wants some better “HTML5” demos (presumably that work across browsers, and don’t just “use HTML5 as a buzzword”) they can easily make some themselves. Why should Apple be responsible for making sure their Safari promotion showcase works perfectly in every other browser?
As for why they block other browsers: probably some or most of the demos break in some way or another. If a naive user with (say) Firefox visited a page and the layout looked like shit and nothing worked, the user would quite reasonably think that Apple’s site was broken.