Exactly. It appears from what others here have said that Grey makes sure not to hit hard enough to leave permanent marks and the friend who lent it to me tells me that he's willing to change for Ana, but most of the men who get off on this kind of thing won't ease up... and the women who stay with them, convinced they'll "change" like Grey did, will pay the price.
In fact, one of my friends who has read the whole series and was really disappointed with the way it ended said "If that guy weren't a billionaire, Ana wouldn't be so willing to go along with his 'red room of pain.'" To be fair, though, he's also supposed to be really hot, and in the beginning Ana keeps harping on how good looking he is constantly. For some women, that's all it takes.
Another thing that annoyed me was the poor writing style. Ana's inner dialogue is maddeningly rambling and repetitive. I feel like the author just wrote this off-the-cuff - there's actually grammar errors in there! Did the author even have an editor? But since it originated as Twilight fanfic and was a spawn of the author's fantasies about Edward as "dom" and Bella as "sub", I guess we shouldn't expect Shakespeare.