I agree with you, in that change is almost always resisted and when forced is almost always criticized. I can't speak to changing from Vista, because I haven't used it and it hasn't been used at any of the places I have worked (which has only been two companies in the last 9 years).
But, I can speak to the change from XP. I have beta tested Win7 for about 6 months, and in my opinion the normal user will be impressed with Win7. If you are comfortable with XP (especially if you like or love XP), becoming comfortable with Win7 will be a very short leap. The very basic feel and functionality is similar to XP. So the average user will have very little dificulty adjusting to performing the same functions in Win7. Once that short adjustment period has passed, they will start to explore. Then they will find some of the cool little bells and whistles (the ones that probably won't really improve job performance). Which will change their perception a little more. If they were happy, they will be impressed. If they were on the fence, it will probably help sway them. If they weren't happy in the first place, they probably will continue to be unhappy (and probably would be no matter what). Once they discover the bells and whistles (fluff), they will explore some more. Maybe they will ask questions or use their own initiative and do some browsing/research. Now they will find ways that it can improve their productivity, by making things easier or allowing them to do things they couldn't do before (either because they didn't know how or because it couldn't be done before). In any case, it all adds to the experience.
I am not a psychic, but I don't think it's a stretch to believe that Win7 will be accepted as much as XP is. I don't think it is a stretch to believe that it will be liked better than XP is/was. You will always have resisters to change, and some of them will go to any lengths to fight it. But those individuals, for the most part, probably do that with everything and it is part of their nature.
In this field (of technology) you either embrace change, burn out or become non-productive. It is going to change whether you like it or not. Some changes don't turn out to be beneficial, and sometimes you don't see that until after the fact.
*** Does anyone believe this is going to be one of those cases? If so, have you actually used Windows 7 for any length of time (beta/RC)? I have, and I can't imagine that it will not be better liked than XP by average users or support personnel. But I guess only time will tell if I am right or wrong. But time will tell, because it is coming (or rather, is here).