I'd suspect that it's not so much about abuse as such, more about control. Whether you are dom or sub, you are in a situation of force and coercion which is at the same time completely safe and enjoyable. Its a way of taking the bad memories and making something good out of them.
My ex-slave had had massive ongoing surgery in her childhood, and I often wondered if that had something to do with her being a pain-pig. Certainly, any time I thought twice about hurting her I remembered that life had already tortured her worse than I ever would.