cadetmatt, I think notsmallmatt really answered the question in his post.
You are correct, yes, a vagina is pretty well designed to have a penis fit in it. But also think of it this way: imagine the ugliest, least attractive female you can imagine. Is her vagina as attractive to you as the one owned by the hottest, most gorgeous female you've ever seen? Of course not. It's still a vagina, but you are less attracted to it.
Sexual satisfaction encompasses so much more than just a hole to shoot your load in (or for the ladies, so much more than just a pole to poke around in her pussy). All the senses are involved: scent, sound, touch, visual... it's the various combinations of all these things that will determine whether or not you find a person attractive.
I have dated women, and I have had sex with women. Unlike some gay guys, I don't find it to be disgusting. It's just not very satisfying. Another example I could give is this... if you masturbate, by yourself, you can have an orgasm. If you masturbate while an attractive woman gives you some additional stimulation (kisses, touching or nibbling your balls, letting you suck her nipples) is that orgasm not better, even though you are technically still doing it yourself with your own hand?