Ok so I get that its great for the pipes but it would seem to me that you would just have to over-eat it to build muscle???

Building muscle takes adequate caloric intake and cardio burns calories. If you do tha math it seems that whatever you burn in cardio your going to just have to eat more to compensate for, if your main objective is to build muscle.

So why do the pros all do so much cardio? even when they are not prepping for a contest?