I used to wonder this very same question,  especially when I would see ads for post op t-girls.  I then realized this question should fall into the "who gives a sh#t" catagory.  Why are some men attracted to very large women? Why are some men attracted to women with blonde hair?  It's all a matter of taste and no one can explain that.

Well your right in saying there are lots of complexities to all this fascination men have to both Pre-Op TSs and Post-Op TSs. But you can't just say it is all because of the eh..hemm "unit?"
I mean why are there so many differnt types of providers out there?, Beauty is wherever you find it!
I know a lot of guys come to me because even though I am just like any other female, there is still an air of taboo with me. Other guys see me because they do see me as just another female provider, and some men rationalize that because I am a post-op and dont have a penis, they  are still safe in thier own sexualty. Even though I personaly don't feel a guy would be gay just because he saw a pre-op. Another thing is I NEVER take my femininity for granted like some genetic women do. I celabrate the fact that I am finaly the woman I was suposed to be all along. So I take care of my body and spirit everyday.I know I am just starting to break open  the seal here, and I am sure there are a few guys around that can add even more to all this?

I think for a lot of guys, it's the whole "Wonder what that'd look like, feel like, etc?"

As Kylie said, it's pretty well known that both Pre- and Post- op TSs tend to "work their femininity" a little more than GGs.

Finally, while I can't say it's a universal thing, but most men see TSs primarily because they like some aspect of the whole TS thing. For some it's being topped. For these guys, a post-op brings nothing to the party. But...for a guy that appreciates the knowledge of the male physique that TS's possess, a post-op's lack of a penis is sometimes a plus.

In addition, many guys like TS's because they like the tight sensation of anal sex. In many cases (though I can't speak for all), post-op girls are equally open to anal either because their pussies are not as resilient or out of habit/preference. Again, the lack of a penis part can be a plus for some guys.

So, like most things, there are many reasons.

For most though, it's the variety card.

Just my thoughts...MC Ess Var

I was tricked my 1st time,
vannessa/lisa
nuvia/nancy/esmarelda/lalani/selmah/bella
and many more
i was just curious after that.
post op are not womanly its just a fantasy

To me, it boils down to basically one thing -- femininity, with confidence in who they are running a very close second.
Yes, a coy and playful submissive spirit, intimate moments, along with possessing an uninhibited innocent aura about her, make the whole TS encounter and fantasy come together also, but it ALL still hinges on how feminine her behavior and attitude is, be she a pre or post-op.
I've yet to experience my first encounter with either type of transgendered beauty, but I must assume as a virgin at this point that an encounter with a pre-op would offer a level of anticipation and excitement much different than an encounter with a post-op, as the pre-op encounter would present itself with a world of thoughts, feelings, and well, possibilities, I never knew existed before. On the other hand, I suspect just the novelty of an encounter with a postop TS would also bring about a level of beautiful excitement Ive never experienced before also ... Heck, I've gotten a big high from just conversing to a couple of feminine, sexy TS women over the phone in the last few months, be they a pre or post-op.
Summarizing this: To me, it is more about a TS's feminine attitude and behavior and not whether they possess a cock or not. That's secondary. The most potent aphrodiac is that which developes between our ears I guess, as well as different strokes for different folks, huh ?
Whichever TS I encounter first, I'm sure it will be time well spent.