Masculinity and femininity are not totally physical characteristics. They are as much personality traits, or chosen behaviors, that influence the way we are perceived, as physical traits in themselves.
To the degree that your question is strictly about physical appearance, hairlessness or physical slightness are no indicators of the position preferences of the well hung. I suspect, however, to the degree that those appearances are enhanced by behavioral choices, femininity is one way that one might signal one's interest in bottoming. That is what possibly lies behind your anecdotal observation.
Please note that I did not say all bottoms are feminine, just that it is certainly more common for "fem" types to be signaling their interests as opposed to just being randomly born that way or doomed by their fair features to always "catching." | 
