The sad thing is that many sites can't even get basic keyboard support right, and that's something HTML handles quite well.

Classic example is Tab ordering. When I hit Tab, I should reach the most prominent and useful field immediately (almost always a big fat search field). But too often, my first Tab lands me somewhere useless, and if I'm really unlucky it even scrolls me all the way to the bottom of the page to reveal a stupid field in a signup form from an ad or something. 5 or 6 Tabs later I may eventually reach the Search field that was in the top-left corner of the page.