Windows 7 is heavy in a sense.
All Windows 7 is is Vista, but much improved. Most of the issues were fixed when the SP hit for Vista that were haunting users. Windows 7 "appears" to be faster than Vista. In actuality, they are the same performance, only UI (user interface) changes have made it appeared faster. So with that said, XP is obviously going to be faster simply because Windows 7 does way more than XP.
But why would you want to continue using XP when Windows 7 not only supports more intense hardware, but obviously is going to get more support because it has rails for XP *and* 7/Vista?
And to my understanding, all it's saying is "ha ha, XP is still faster" (but with browsers....)