XP is slim and minimalist.. the standard user just want to use the tools they are used to.. also XP will be economic about the machine resources it use..
Security for instance its more of a hacker thing.. to a more technical aware audience.. and we are a minority, in the tech consumer market..
I i were MS CEO i would have created a branch from XP and advanced in two lines of OS.. win 7 family and a XP family, of a more bare OS with less obnoxious things and that could bootup fast with a minimal UI..
I dont know what happen with tech companies down the road, that with time they forgot this minimalism, this zen way of doing technology that probably was the thing that make them sucesfull when they were tiny and irrelevant..
I think, thats one of the secrets that have maded Steve Jobs so sucesfull in the things he were doing..
So if we think well about why people stick with XP, its not just about the OS they got now.. but because of every "evolutionary" step in new OS's nothing really appeal to the real life user (not us, tech people and power users)..
Sometimes even the "new new" sometimes its a step behind, in terms of what the OS really offer.. (compare what you got with XP for instance versus ChromeOS)