A female friend of mine, whom had been visiting from out of town, was chatting with me about how generous it was for her host to forego sleeping in his own bed so that she could make use of it while in town. She reflected that she probably wouldn't do the same were the situations reversed and I observed that it was fine because what is "fair" isn't necessarily what is equal.
By using the word "fair", I am using a word that really isn't fully fitting the situation but it illustrates by analogy fairly well. I meant to say that I could see his valid reasons for doing so: that it was a means of expressing appreciation, esteem, and regard for her comfort as a magnanimous host. (i.e. probably not an ugly sacrifice)
Representing here only the male view, one of the ways that we respond to value in females (even if we're just friends) is by acts that I would more-or-less classify under the umbrella of "chivalry". That term has a lot of historical baggage involving people wearing metal suits but if we can discard the duty notions for a moment, and just focus on the essentials of the acts, I think it solidify my discussion.
So what are some modern examples: Opening and holding doors. Offering a lady your arm while you walk. Pulling a chair out for your partner to be seated. And the one we've listed above. What are the essentials here? They all involve physically reducing effort, exposure, or danger on the part of the chival-ree and, ultimately, are acts which express esteem by means of contributing to an increase in safety and comfort for the lady.
And it doesn't work with the genders reversed. Not sure I want to get into that, but I'll simply state here without any supporting documentation that you'd gut masculinity if it were reversed, barring any special medical conditions. I don't as much cover the other end here, but women have their things they do which men feel special too that are particularly charming in feminine ways.
I think this is awesome. It's completely unequal and yet completely sensible. It is a way to express your gender identity along with your moral identity if you do it right (i.e. not out of a sense of duty but rather as a generous response to value). I think it speaks well for us that, as an American society, some of us are still down with this and can still see and act upon the beauty in our gender differences. To the ladies in particular, thanks for being good receivers of our good will.