I'd just like to expand a bit on Nick's post that resides just below this one and on the basketball article that sparked it.
First off, I'm going to respectfully diagree that the NCAA Tournament's popularity is "primarily driven by gambling." I fully acknowledge that there is considerable wagering interest in the game, both by entrants in office pools and by Vegas pros. However, I think the event is great sports and great theater even stripped of the gambling context. Sure, filling out a bracket gets casual fans interested, but anyone with even a passing interest in basketball finds this competition compelling.
Second, both Nick and Kelly Dwyer make the point that NBA players are simply better and that translates into higher quality of play and entertainment value. This point I agree with - there's a reason why people pay the most money to see athletes compete at sports' highest level of competition. NCAA fans bring out arguments about how they're kids and the sport is more "pure": that latter claim I find both incorrect and irrelevant. If a good game is played well, it's generally fun to watch; the NCAA tournament is a good game played well, the NBA is a good game played much, much better.
Third, I'd like to expand on Nick's excellent point about how the NCAA basketball tournament often awards the title to a team that is probably not the nation's best. Obviously a quality team always wins, but it's more the school that catches a hot streak than the true "best" team. The single-elimination format is exciting as hell, no doubt about it, but it naturally produces lots of flukes and cheapens the thirty-game regular season. The NBA's grueling series format ensures that the team left standing in June is truly the most deserving club.
What's interesting is that commentators hold the NCAA tourney up as a model of proper championship determination and at the same time decry the BCS system responsible for doing so in college football. Grumble as people may about pollsters and computers deciding the key matchups, it's almost indisputable that every year one of the nation's top two teams claims the title. Look at the recent winners: LSU, Florida, Texas, USC - there's no question these were the top teams. This particular success of the BCS (among others) is a fact that far too few people credit properly. It's easy for talking heads to spout off populist rhetoric about how they want the championship decided "on the field" without stopping to recognize that all those games played in the regular season (on fields) are what decide the title game's participant and ensure a worthy champion.