Don't you think you're gettng a little too heated and overanalyzing when it comes to some books you find in the young adult section of barnes and noble?
Vampires are fictional so by that very nature there cannot be a right or wrong version. And every movie and book has had a different take on them. In some, they have sex. in others, they don't. In some they can't cross running water. In others, they have little restrictions. In some garlic will keep them at bay, in others, it will just make you smell funky. in some, they can go out in the day if they are weak, in others, they can't - ever. in some they can turn into other animals, in others, they cannot.
The idea of blending sex and vampires has gone back a long long long time. it's a natural comparison. There's penetration, sucking, and erogenous zones involved. In the book Dracula, those vampires have sex.
People need to relax...it's four books of harmless fiction writted for the appeal of teenage girls.