This is an expansion of Ebbixx's point about universality. I have read (possibly in books by Poitras, Levy, Napier),(but have yet to see) that there are many quite explicit homosexual anime and manga whose target audience is female, and that this practice is considered entirely normal. I am no expert on Japan or Japanese culture, but this example definitely points toward a lack of universality on a cultural level.

Perhaps this fits with lioncub's argument that women may not be turned on by gay porn because there is no hope of joining in. cartoons are imaginary people who are neither gay nor straight in "real life", and as long as the viewer suspends their disbelief far enough to be turned on by animation, this difficulty of imagining oneself into the sex disappears.