Aliasalpha: From what I've read, its justified as part of the story and is actively designed to make you uncomfortable rather than titilate so the traditional issues of nudity aren't really relevant.
Also this might just be my rebellious and selfish nature coming out but I've always been of the belief that choosing to not do something that is harmless and that you normally would want to (and the preorder is evidence that this is the case) for the sake of someone else is letting them have too much control over your life.
Is playing it when she's not around an option?
I certainly do not want to start a flame war - only sell the game and try and re-coop some of his money, but harmless is subjective. He pre-ordered without checking the rating on the game and would not have ordered it if he had. So he really doesn't want to play it. We all bow to some level of control if you want to call it that. I see it as a choice and he is making the right one.