IE9 uses a new hardware-accelerated 2D drawing API called Direct2D (kind of a replacement for DirectDraw) and a new text API called DirectWrite. Neither of these is available on Windows XP, precluding IE from being easily back-ported.
So pretty please, with sugar on top, stop making flippant demands for multi-billion-dollar companies to do things you don't fully understand the implications of.
It is the place of consumers and web developers to make any demands they please of any multi-billion-dollar company they like, regardless of their understanding of the issues. It is the place of the multi-billion-dollar companies to decide whether to honor those demands.
Also, it's not terribly difficult to support more than one drawing API as long as you abstract the drawing code, as is most likely done for Direct2D in Firefox 4.
I was actually referring to the original article, namely IE9 on Vista+, with my flippant comment.
But now that you mention it, I guess we'll just leave it up to the Other Browsers to put accelerated 2D on XP. They're open source if MS wants to see how they did it.
So pretty please, with sugar on top, stop making flippant demands for multi-billion-dollar companies to do things you don't fully understand the implications of.