I agree with what you've said. But I've wondered if it still could be called "abuse" if she's consented to it. She was also told so many times in this book by Christian that she could leave if she wanted to; so there were always so many opportunities to pull out if she were unhappy.
I'm not talking about the sexual side of things, I'm talking the full on mental abuse. Many of the people I spoke to after reading the trilogy loved Mr Grey, especially after she had succeeded in "changing" him - this got me wondering how many women actually in abusive relationships would stay with their partner, because there is a chance he would change. You can say that they could leave if they wanted to but most don't. To tell you fully why I was left with these thoughts I'd have to read the trilogy again - something that would pain me because of the poor writing I had to sit through for three days!