I interpreted that final scene differently than you. She's not manipulating him at all. There's no motivation to manipulate him. He can give her nothing. I'm going to be vague here, even with the spoiler filter.
What happens, in my view, is that she finally recognizes that he was the best of the (bad) bunch and as a way of thanking him for returning the "R" to her, she offers the only thing she has to offer. She only then realizes (I don't know why you think she's recognized it previously -- she's had blinders on) that he has feelings for her and that perhaps she feels something for him too, and the entirety of what's gone on over the last few days and what she's doing with this man all catches up to her at the same time. It's a wonderful scene, with great acting from the two.
In general, I think people are caught up in the sex and madcap comedy (which was funny), and are having trouble grasping that the presence of those elements doesn't mean the film isn't good or serious. Everybody's entitled to their opinion, but count me out of the "akshully, the Oscar winning movie sucks" camp. I'm in the backlash-against-the-backlash camp.