Well indeed, Vista was replaced quickly. Some people say Windows 7 should really have been Vista SP2 (before Vista SP2 actually came out), and in reality a lot of the bigger changes in Win 7 have been in the user interface and experience rather than the underlying kernel and system architecture. Given enough time a lot of the improvements in 7 could have been tweaked into Vista, but I guess we'll never know. At the end of the day though, given a decision between putting Vista and 7 or XP on a machine today, there's no real reason to go Vista at all.
Oh, yes, I was actually looking forward to WinFS
