First, I want to make it absolutely clear that college is more fun than b-school, for the vast majority of people. However, there is a subset of people for whom a top MBA experience will trump college. There is obviously a lot of overlaps between these group; in no way are they mutually exclusive.
1. Overachievers who went to elite undergrad. These people are the good chunk of the student body at top schools. While state school kids were getting wasted and tailgating, they were working their butts off, getting that high gpa, piling up extracurriculars, and then dominating their demanding jobs. For them, b-school is their reward for their hard work, where they can blow off steam.
2. People being sponsored and returning to their employer. This is a coveted group, and everybody hates their guts. These are the guys who often skip classes, go out 4-5 times a week and could care less about how many people from their class got that mckinsey offer.
3. Smart nerdy types who don't quite fit into a college social scene. Some people, for whatever reason, just don't fit into most undergrad environments. Maybe they don't like typical college parties or are too socially insecure. I know a lot of these types who actually blossomed in b-school and had a great time. Maybe it's the b-school coccoon, where you are surrounded by so many people with similar interests, hobbies, and ambitions.