It is possible to have both. Just not fully functional. A clit and a cock come from the same groundwork, and the ovaries and testes come from the same groundwork. So you could have a very large clit that looks like a cock, and a vagina, but most likely that cock couldn't piss, and likely wouldn't cum, unless the testes were just inside, in which case you could ejaculate semen (I don't think sperm could be adequately formed inside the body), but couldn't be impregnated. Yeah, I don't know why I felt the need to say that in a couple month old thread, of a forum I just started on, but yeah.
Oh, and the appeal of shemales: it isn't just tits and a dick, there's more to the female form. If she/he's a really good-looking trans, it will look like a female, sort of like that Mint, just be hiding a cock, and I think that's the underlying appeal, the female but with something to hide. The taboo.