reverse punch defense

Often times in the dojo, we practice defense off a punch with the offender stepping forward and punching. The idea of this technic seems to be to remind the defender to keep a good distance away so that the offender must make a huge body movement if they are to make contact thereby allowing for reaction time. However, when we spar, we are in much closer range to our opponent and they never seem to step forward to punch. I would think that with practice, a person would be able to increase their reaction time to be able to properly defend a reverse punch aside from merely blocking it. It would be as if I tried to hit a baseball thrown by a MLB pitcher; I would invariably strike out. But start slow and over time (years that is), I should be able to connect with a high average.

This is all theory at this point. Has anyone proven this theory? If my theory is correct, then why do professional fighters (ex. UFC, boxers) allow their face to be cut up and their ribs to be broken?