What is the essence of art?

I read an article in the New York Times on Sunday about body types and shapes versus actual dancing talent and skill ("Funny, You Don't Look Dancerish," May 20, 2007, Arts and Leisure section, p.26). While a number of people are able to look at a dancer as someone who dances, rather than someone with a particular body type, most (implies the article) cannot. And this includes the audience.

Why is it that dancers must look a certain way in order to, as some would have it, dance "properly"?

Interestingly, writers are faceless (for the most part). Musicians come in all sorts of shapes (although it does help in opera if you have movie-star looks, apparently). But only "lean, athletic" people are supposed to dance. Anyone else seems to embarrass people, no matter how gracefully and confidently they move. Why?

Writers who write poorly are embarrassing. But writers who are fat? Or ugly? Nobody cares! (Something I find comforting, for reasons of my own.) A bassoonist with a big zit? So? A composer with a limp? Yeah, and? A director, an arts manager, a publicist -- all can look however they want. But people who are supposed to be looked at have to look a certain way. They have to be more beautiful than we, in our normal lives, could hope to be. Why are only beautiful people permitted to be graceful and powerful and noble? Why aren't people considered noble for their actions and talents and determination?