Not true. It uses more memory than XP, but it doesn't require it. In exactly the same way that linux uses more memory than XP, but doesn't require it (it's used for system cache if you bother to check). If you actually install the 64bit version, you'll see where MS's development budget has been spent (The 32bit version of vista feels a bit like Win ME in comparison). In every test I've done, 64bit vista has crapped all over XP from quite a big height.
Well, I haven't really bothered to investigate Vista fully. I use XP as a gaming platform and I use Debian profesionally (and I use Ubuntu at home for variety). Vista firstly just pisses me off with its change of interface. It feels like you have to be both stupider and smarter to make it work.
I do find it hard to believe Vista gets the same performance as XP. As you say, Vista uses more memory and I have been given to understand that it's really impossible to keep it from doing that. I also quite clearly remember a line from microsoft saying Visat isn't slower it just does more for you. That's the same thing to the end user. Still I haven't done the benchmarking I just have a feeling. Which is worth the paper it's written on.
I'll stick with Linux for myself unless I really want to play a game.