Rich UI in a browser?

Rocky Lhotka blogs about the "browser wars" and presents an interesting view on it's use:

Sure, some people are foolish enough to use the browser as a programming platform (as in using client-side script to do a rich UI). Those poor people are stuck with IE (or whatever browser they targeted), but that is a poor strategy anyway. Note the total lack of development tools support for client-side programming. There's not a vendor out there who is encouraging or enabling client-side programming. It is a total dead-end wasted investment in the long run.