Rugby does have hits, hard hits that are painful. They are nowhere near as numerous as in American football. There are rare situations that occur in Rugby. You note not calling a mark, and this is a real situation where if somebody screws up they'll get smoked. In American football on every passing play (roughly 60% of the plays) a wide receiver can do everything properly and still get completely, utterly blindsided by a defender, hit in a position that has no real analog in rugby. And this happens on 60% of the plays.
I just wanted to note that I think the whole padding argument is kind of trite, that's all.