I still don't believe that people think XP is better than Vista. Come on, All you need to do is upgrade your Rig so that it can better support the amount of resources Vista needs. But truth be said, XP is most popular because it's really lightweight. And I love it for that when it fits just nice on my Laptop.
Now that Windows 7 meets almost all the advantages XP has and drastically improves Speed Security and Stability, it is no surprise that most Corporations will switch to it. Hopefully my school computers that still run XP will be upgraded to 7.
Lastly, I think your sources are a little over-exaggerated. Not all corporations will be quick to switch to it until all applications are 100% compatible and drop support for XP.