Katy from Captive Heart responds to the discussion below by writing:

It’s when communication between the sexes gets complicated, that I’m glad not to be in a vanilla relationship. See, when Master wants sex, he takes it. And when I want sex, I beg. We’re never in doubt about the other’s intent, and while we may occasionally have misunderstandings, they are never about sex.

Sounds peachy! Of course, this might not work for couples whose relationship power dynamics are less explicitly specified….