YES. In fact, in Japanese there's a particular saying for them: Fujoshi (Girls who like seeing Yaoi/Yuri eventhough they are straight), and Fudanshi (BOYS who like seeing Yaoi/Yuri eventhough they are straight). These groups have their own genre and circle, and has been regarded as normal occurence. Particularly Fujoshis, because there are MANY.
Scientifically speaking (thanks to ASAP Science), everyone is actually born with bisexual bicurious tendency. Because penis started out as vagina first. That explains why everyone tend to show a degree of attractiveness to the same gender, though the level varies. Hence why there's a term Bromance and the likes… ::)
I agree with everything said here. Porn is just porn: I don't think that it identifies a sexual orientation.