I think this is pretty dead onFor me and my wife there is another aspect here too. She doesn't particularly -like- pain a lot, but she -loves- feeling submissive and possessed. On the other side, I love feeling dominant and possess(ing?)
So for us at least, the inflicting of torment isn't really -about- the torment, if that makes any sense. It's about my seeing how she willingly submits to -me-, about my joy in seeing her submission to me, about her seeing/feeling that joy and feeling joy in return for pleasing me/submitting/feeling possessed. It creates an "emotional feedback loop" if that doesn't sound too trite, in which torment is merely the catalyst, rather than the ends either of us are looking for.
/ramble off