Don't Expect iE9 to Ever Reach XP: Microsoft
That means, Microsoft told the Register, that you won't be able to get IE9 on Windows XP. Based on last month's Net Applications data, Windows XP ran on 52.1 percent of all Windows PCs used to browse the Web last month, while Vista accounted for 27 percent and Windows 7 for 20.8 percent. That's in the U.S., and XP has a greater share outside America.
Chrome and Firefox are still able to leverage HW acceleration on XP because they use different methods. Chrome implements uses OpenGL graphics APIs for rendering; Firefox uses an intermediate layer to work with DirectX 9 and OpenGL.
Of course, the current release of IE9 is a beta, and it will take time to reach release status. During that time, Windows XP market share will drop, as it has been. Still, it seems a poor move on Microsoft's part to exclude so many current users, particularly outside the U.S., where migration to a new OS takes longer.