In the last few years, I've started playing as a female in game that give you the option. I've not put very much thought as in to why, but it's not the butt thing. I don't treat my character as a puppet, I definitely embody her.
I grew up in a place with very rigid (maybe that's the wrong word, english is not my native language, especially when it comes to queer theory) gender norms. I never really felt that I fit into that version of the male role, and still don't feel like I do. So perhaps my choice to play as a woman is more about not playing as a man.
Then again, it's not just that I feel more comfortable playing as a woman, I actually LIKE it. I have a friend who recently came out as intergender, and that actually makes a lot of sense to me. Either way, it certainly feels like video games (Skyrim and Saints Row in particular) has allowed me to explore these issues from a more... well, internal point view I guess.
So, yeah. I guess that answers the question?