From what I have read Vista is more of a stepping stone OS than anything else. A lot like how windows 2000 was a stepping stone to XP. It was put out to be the OS that bridge the gap between XP and true replacement.
Best way think about it is something between OS9 and OSX. Unlike apple Microsoft can not make that leap. MS bread and butter is the business market which moves a lot slower. Apple bread and butter is the home user market.