Watch King Mo vs. Rafael Feijćo for the SF LHW title and maybe you'll get your answer.
Btw, I'm not trying to say that body punches are useless. Quite the opposite. You can use everything on MMA as long as you know what you're doing and you know what your opponent can do to counter it.
Mo actually had success early with his body punches. I think Feijao would end up gassing due to the body punches but Mo got in love with it and was trading knees to his face in order to land the body punches.
EDit2: On UFC 120 Maldonado (former boxer) won by tko due to punches to the plexus(sp?).