Debris getting trapped in the tread is only a problem on the front tire of one of my bikes. I learned the hard way to make sure to clean those sharp little stones out of the tread or they will eventually work their way throught the tire and puncture the tube.

The back tire on that bike is a different style, armadillo, so there isn't any tread to trap anything. My Jubile Sport has tires with really close together tread, so nothing gets trapped.