T-Girls are special - Femininity is a tremendous satisfaction for T-Girls and most love the attention from a gentleman admirer. Notice the word "Gentleman?"
A lot of guys who show interest in TS's are, in fact, bisexual. Others are bi-curious. Still others are looking for cheap thrills.
Some men find TS's to be more feminine than GG's. And then, of course, there are guys who seem to just plain connect better with a pre-op transsexual than a GG.