I think it really is a form of submission, since you aren't exactly dictating to them how to treat you; just trusting them to use/abuse you in ways that you're willing to submit to and that (at least) they'd enjoy.
'course, it's better when both enjoy it, but since you're supposed to get that intrinsically from the setup, it's at least less of an issue.
Me, I'm more of a selfish bastard... but I don't like that.