Okay, this is a topic that's been coming up a lot recently. There have been already been a ton of great posts like this and this and this , so I'm not going to go over why this trend of psuedo-rapist love interests is a Very Bad Thing.
Instead, I'm going to talk about why I think these books have become so popular.
Paranormal books are (mostly) about escapism, for a lot of people. They whisk you away into magical adventures with magical creatures that you wish you could see and talk to.
Or do you? Most of these books (for instance the Wicked Lovely series by Melissa Marr) involve extremely dangerous creatures who hurl the main characters into life-threatening situations. Often friends or family members die, or at least are put in extreme situations. The main character has to grow up fast and make hard choices.
Do you really truly want to live in that world? Probably not. And yet we gobble up books like Twilight where the main character has her uterus ripped open by someone's teeth.
I think that the romances in paranormal books operate on this same principle. It has to be more extreme than real life. If someone were to hop into our bedroom at night and be like "Oh hai there how ya doin", we would be mightily freaked out. If a guy sexually assaults us, trust me, we will no longer find him attractive. Ever. Real life sexual assault is horrifying and frightening and demeaning.
But in books, this romantic intensity operates on the same principles of all the rape books that were so popular in the 50's and back. Girls like the idea of a boy being absolutely overcome with need for them, to the point where the girl can keep turning him down and he'll come back. In real life this doesn't happen because if we like someone, when they ask us out we go "YES PLEASE AND THANK YOU SIR". There's no chance for a guy to go to extremes chasing us. Books like Twilight and Hush, Hush let us live the fantasy without ever having to be in danger or discomfort.