Q: Is there any reason why there is such a big incidence of pec tears during benching in comparison to shoulder/triceps/lat tears, especially if powerlifting style is supposed to de-emphasize the use of the pecs?
A: Research at Indiana University found that cross-sectional area of the subscapularis is the best predictor of powerlifting performance, believe it or not.
If you're getting that much hypertrophy of the subscapularis, it's doing a lot of work - and for a small muscle. Ask any manual therapist, and they'll tell you that subscapularis is always balled up - and frequently shuts down due to repetitive microtrauma.
Shut subscapularis down, and pec major will work overtime as an internal rotator of the humerus. Reference Shirley Sahrmann's work ; if you see an strained/tight muscle, look for an underactive synergist.
You'll also get a humeral anterior glide, and additional tightness/restrictions on infraspinatus/teres minor.
So, the name of the game is to activate subscapularis with exercises like those in Inside-Out , and also improve the length and tissue quality of your external rotators.