A few weeks ago, Dean Hachamovitch, the general manager of Microsoft's Internet Explorer group, went on the record declaring the company's support for HTML5 in Internet Explorer 9. The Internet community generally applauded his remarks, although there was some consternation about his statement that IE9 will only support H.264 video. However, one point was generally ignored: IE9 will only be available for Vista and Windows 7, not for Windows XP, nor for any other desktop platform. It's not even clear that a full implementation of IE9 will be available for Windows Phone 7, which may well become a tablet platform in the future.
Microsoft claims that IE9 won't work on any platform besides Vista and Windows 7 because of the "magical" acceleration features they're using in the operating system. Bulls#!t. Firefox, Chrome and Opera are all cross-platform and all work much better than IE8. The reason that Microsoft will only support Vista and Windows 7 is that, as usual, they want to encourage upgrades to Windows 7. Thus, Microsoft is all for HTML5, but only if you buy Windows 7. If you're running another operating system, they won't support HTML5 at all.
Microsoft's corner of the universe keeps getting smaller and smaller, largely through the company's own actions.