Well as I have a tendency to write a thesis whenever I post on a subject, I will simply put it briefly for now, and save everyone the hour that it would take to read my post.
I think that the appeal of Transsexuals, is that to an otherwise straight man, they can be perceived as women that has the sex drive/mentality of a man. A lot of trannys enjoy being objectified, where a lot of women do not. This isn't to stop a man from objectifying a genetic female, but there is more of a honesty with the Transsexual, and that is probably a transcendental quality to those whom find that aspect appealing.
IMO it is more of a fetish for straight men, then anything else.
I may yet decide to go ahead and write another thesis on the subject...lol.