I don't doubt that there's a tremendous performance difference, not one bit. But will you agree that 7 isn't substantively different from Vista apart from the critical bug/performance fixes?
But then, having made Vista so different from XP it would have been commercially and technically suicidal to have another substantive shift at this stage. What they needed, and in fairness what they have done, is to consolidate and perfect the Vista base to a point where production environments could have confidence in adopting an up-to-date version of Windows again. Lots of businesses never upgraded from XP to Vista and this will have been a huge blow to Microsoft's expected revenues. To fix that Windows 7 had to show stability and consistency, not a whole raft of radical changes.
Regardless of what many people think, Microsoft have been at this game a long time and they have a decent grasp of what they are doing. It may not be everyone's cup of tea, but never assume them to be stupid.
