Why do men love using women's lap as a pillow for comfort and trust?

A good way to show the physical intimacy and trust which a couple have is to rest one's head on the other's lap. Usually, the man does the resting while the woman provides the lap, not only because of anatomical reasons but because the lap-owner is typically of a nurturing nature more associated with femininity. Bonus points if she's feeding him grapes or stroking his hair. I found that be weird, but what is so romantic about that.