I think it may depend on whether they were born male or female.
Liking shemales is totally normal for straight men and doesn't indicate bisexuality. Straight men love their cocks, but they also love women. A woman with a cock is like the best of both worlds. The fact that the cock has to be on a woman proves that they are still straight, and simply really enjoying the concept of cock because they like having one.
http://slog.thestranger.com/slog/arc...ter-of-the-day
Excerpt:
"Your boyfriend's interest in shemale porn and, presumably, shemale persons is not evidence that he's gay ... rest (somewhat) assured: Gay men aren't interested in shemales or shemale porn, and gay men don't patronize shemale escorts. Shemale porn/escorts are almost exclusively consumed/patronized by straight guys who are into cock, or would like to get into cock, but are absolutely, positively not into other dudes."
I know that's not really an answer to your question, but you sounded a little unsettled about admiring the she-male, so I thought I would set your mind at ease.
Honestly, even as a straight woman, it's hard to argue with the potent combination of boobs AND penis. Usually in porn, the men are unattractive, but the women are beautiful. Attach a penis and TA-DA: hotness.