I think media capitalizes on attractions which are already there. For very primal, almost instinctual reasons, we are attracted to health.
edit: Women tend to be less visual than guys however.
This doesn't explain why "health" seems to manifest differently at different times and different cultures.
Even today, calling a girl "healthy" looking usually means she is pretty thick -- and not in a "super buff" way. For the most part, I think this is a post-facto analysis that we overlay on our attractions to justify them.