Its an audiences, mostly guys looking for some sort of online relationship. All you need to do is moderate a live cam chat in one of the solo sites to understand.
Some may love the girl and sign up just for her looks, but its pretty safe to say that solo site traffic is pretty close to the same traffic as one might send to a dating site.
My experience is, that once a girl does hardcore in her solo site, the mystery is gone and retention and interest will drop. Its all about the tease with solo sites.
Just my .02
