Cinci doesn't "get away" with being physical as much as they beat the system (and refs) into submission. It's a well known that statistically fouls are called far closer to even than an unbiased called game should result in (particularly if you take away skewed data from end of game intentional fouling). And you can measure the likelihood of the next foul based on who the previous fouls were called on, what the total "count" is, and who the home team is.
This means in the aggregate there is little penalty to being a more physical team. The stats say you will not be punished as much as you should be. So if the other team fails to adjust the style of play - you have a huge advantage.
Additionally, other studies have look at "setting the tone" of the game. If you start off physical a few calls might be called early, but it isn't long before the refs get tired of calling fouls and want to let the game "flow," or the urge to keep fouls even kicks in. It's the same reason why a guy who constantly carries, travels, or sits in the lane for 25 seconds doesn't just get called over and over and over.
The NCAA tournament may seem more physical because more physical teams often make the tournament and know how to use the system to their advantage, that and refs wanting to "stay out of the way" at important moments and in big games.
Really dry (but interesting!) statistical paper on the subject:
http://home.kelley.iupui.edu/kyjander/Officiating paper - Final draft version.pdf
This study examines the pattern of foul calls exhibited during 365 NCAA basketball games during the 2004-2005 season. Results of the analysis indicate that officials are more likely to call fouls on the team with the fewest fouls, making it likely that the number of fouls will tend to even out during the game. This increased probability increases as the foul differential increases. In addition, there is a significant bias toward officials calling more fouls on the visiting team, and a bias toward foul calls on the team that is leading in score. The result is that the probability of the next foul being called on the visiting team can reach as high as .70 during some game circumstances. Finally, implications of this officiating bias are explored, including the fact that basketball teams have an incentive to play more aggressively, leading to more physical play over time.