I think that, technically, it's called "acting." Gestures have been part of acting and oratory for many centuries (it's called "chironomia") and reinforce the actor's response in the scene. We all do it, it's part of our culture; actors do it because acting is, after all, exaggerated reality. (If you doubt that, sit in when a disc jockey is broadcasting on the radio and then listen to how the person sounds when not on the air.)