First, do this: run your mouse over the buttons on Google's home page. (There are only two of them.) We've all had drummed into us that every .gif needs an alt text for the purposes of accessibility. Hmmm. No alt text appears.
Now, look at the source code to confirm that the buttons don't have alt text. Hmmm. No buttons. At least, no "img" tag. There's a lot of code here, and I can find this:
<input name=btnI type=submit value="I'm Feeling Lucky">
But there's very little here that I recognize as standard html. I tried running some basic accessibility tests on the page (I'm no expert in this area, so my tests may have been too simple) and there were some errors, but none of the ones I saw were considered terribly important. I don't know, however, if the accessibility testing software understood the Google source code, nor if typical screen reading software would be able to determine from the code that there are buttons and that those buttons have names. So if anyone has any insight into this, I would be very interested to hear it.
Note that all of Google's pages seem to use this non-html style coding. I'm willing to believe that it is more efficient this way, but I wonder about what it means for compatibility, for competition, and for users.