Sorry guys, but I see this thread is a tad much ado about nothing.
First of all very soon all browsers will adopt htlml5 with more and more features, because no one want's to be left out of the future, ie has already publicly stated their support, and so have opera, and firefox. I don't care about chrome.
Secondly, in terms of adoption, I don't see any problem when for years we've been pestered about downloading the latest flash plugin to run flash, it will be very easy on all browsers to prompt the user to update informing them that they might not be able to view the latest standards otherwise. Ff, opera, and safari automatically prompt for updates. So, I don't see why anyone even in the legacy machine(well, not on the lisa...) will be left.
so, like I said, much ado about nothing, apple released some demonstration of features for developers to spread the word about html5 and advance its use. The point is to show where technology is heading, not were it is or has been.