Probably. On one hand, People Still Use IE6. And the people who still use IE6 aren't people who install things like Google Chrome Frame, or the latest updates from Microsoft (obviously). So for the time being, more features, along with cleaner syntax and the rest, means more work for web developers who want to use those features and whose audiences aren't particularly ahead of the curve.
On the other hand, those developers whose audiences are ahead of the curve, or who don't mind the blasphemous "Please update your browser. Here are some good ones:" link, will push the industry forward until the number of people still using IE6, or FF1.5, or Mosaic or whatever, approaches zero. It will happen because people will get annoyed, or viruses, or new computers running new operating systems and browsers. In that way html5 is the best thing that could happen to the web. A backwards-incompatible version will (hopefully) throw the few stragglers, who spend money on the web but still don't need css2, into the 21st century.
My grandmother was, until very recently, using MacOS 9 with IE4. She did not care that her homepage (apple.com, as it had been since she bought the computer) was impossible to read. People still using IE6 and even IE7 in five years will not be the kind of person who spends a lot of time or money online.
