heres a match efren vs hohman, Hohmann commits a foul and did nothing?
http://youtu.be/wmH4ZKNS5q4?t=1h36m50s
right at the 01:37:02 mark.
I don't doubt that he saw the foul. However, isn't it possible that he assumed Efran also saw it, and thus said nothing? Efran didn't take much time sizing up and shooting the combo - perhaps TH only realized that Efran didn't see the foul once Efran got down on the shot, at which point he had the choice to either let Efran shoot without ball in hand, or yell something to get his attention. The second option, IMO, could've turned out a lot worse (causing, for instance, a miscue on Efran's part) given how easy a combo it was, so TH decided to keep quiet.
Impossible to know, but this seems like a reasonable account to me.
this being said, I couldn't care less if players call fouls on themselves or not.