I don't mind if XP is just a (much better, in my eyes) version of 2000. My point is that it's the first overall stable version of Windows to hit the average user.
Vista has not only that to compete with but also the fact that it's the first version that comes with a system requirement of "a new computer".
What do you want people to wait for? For Vista SP1 two years later? Besides, it's not so true because it would take them more than a day to buy a new computer...
Personally, I feel no need to buy a new computer (well, make that computers...) and ditch XP now that I finally found a (freeware!) outgoing firewall software, which was the only thing I hated about XP.
I mean, not having to restart when I install something sounds great, but they'd have to do much better...
My biggest fear though is that like always programmers would only program for the latest Windows' version, in this case Vista. D-day would be when you see the name winVista (or whatever - what should it be really?) next to DOSBox... 😉