In recent months, I have help several people pick out a new city commuter bike. From what I can see, there is very little difference between a hybrid and a rigid fork "sport" MTB. If you put 1.5" slicks on a MTB with a high rise stem, you essenstially have a hybrid. Granted the 700cc wheels do ride a bit different that the 26", but I personally feel more secure with the 26" wheel.

I think MTB's have become so popular with the city crowd because city riding is much more demanding than one would think. And there is a big difference in comfort between a "pro" MTB and a "sport" MTB. They are two entirely different bikes.