i think, required power of hardware have marginally increased at every stage of new OS have been introduced by MS ...
if the prices of hardware will be fallen in future, then we will have powerfull hardwares to run vista as smoothly. we will also have to say " vista is more powerfull system" ..
as logically, Win9x fasterthan WinNT fasterthan WinXP fasterthan WinVista fasterthan Win7(may be..) (if these OSs run on today's hardware).
so, Every OS is best for that particular period of time..
So dont blame Vista.. it will be changed as faster than XP on one stage.
(sorry for poor English)