its also to prevent being badly winded. they breathe to give my power in the punch. and quickly breathe back in to be able to punch again quickly.
its quite a hard thing to develop to do.
No there not retarted as you say, get in a ring with one and see who ends up looking retarted.
Exhaling when you punch creates greater power. Exhaling rapidly tightens your core muscles and helps your body move as one unit more effectively.