No, it's because the men acquiesce. The few times my wife has been angry enough to tell me to sleep on the couch, I've just said no. What happens then is she sleeps on the couch then wakes up a few hours later because it's too uncomfortable and comes into bed next to me.

Our "unspoken rule" now is that neither of us has the right to kick the other out of bed. If one of us is that upset, then it's up to him/her to sleep somewhere else.