Sure the final goal for what we do is for users. You are right in that. At the same time, what would benefit the users most? Having a good, stable KDE in 2009 or making them wait for 2010? We wanted to move as fast as possible. If we wouldn't have released 4.0 in 2008, we would have slowed development (or, not accelerated it) and KDE 4.x would still be a lot less mature.
You can look at it either way - the short term annoyances were worth the trouble. I honestly believe time will prove us right.