I agree with you about the
mostly gay stereotype probably being wrong, and potentially harmful, but I do think it's worth noting that there is a mostly straight paradigm that governs almost every other sport and area of life, that is equally stifling. And I think--even in North America--there are a lot of people who, being straight themselves, automatically assume that everyone else is too, stereotypes aside. (Likewise, being gay, it is easier to think that other people are probably gay, even when they aren't).
The association of homosexuality with the arts is more than a century or two old, and doesn't exist in only one culture. In Renaissance England as well as in Japan centuries ago, there was a tradition of men playing women in the theatres that developed homoerotic elements that sometimes arise within the plays themselves. (For instance, the way Rosalind calls herself Ganymede when she she courts Orlando while disguised as a boy.) Homosexuality was so common in 16th century Italy that the number of investigations was as high as 40% of the population--the punishment was a small fine that was often not enforced; and it was part of the culture there. In Greece, Italy, and Japan, it wasn't considered a sexual identity exclusive from marriage--people could and did do both.
Homosexuality is also associated with numerous poets, playwrights, and artists--Shakespeare, Marlowe, A.E. Houseman, Walt Whitman, W.H. Auden, Oscar Wilde, Henry James, Michelangelo, Sappho, H.D.(Hilda Dolittle), Katherine Phillips(17th c. English poet), Edward Albee, Tenessee Williams, etc. Homosexuality is known to have existed in Native American cultures--"two-spirits" were what would be known today as transsexuals, and were often shamans; there are also instances in African culture. Homosexuality is referenced in Japanese literature from the 11th century; in modern times, there's the playwright Yukio Mishima,
http://en.wikipedia.org/wiki/Yukio_Mishima, and the actor Akihiro Miwa,
http://en.wikipedia.org/wiki/Akihiro_Miwa, etc. Tsuyoshi Shinjo,
http://en.wikipedia.org/wiki/Tsuyoshi_Shinjo, is the guy Daisuke Takahashi talked about recently, saying that if they were ever to talk it would become more than a conversation between athletes. Joe Odagiri, an actor that Daisuke said "has a special aura that attracts both men and women," starred in this movie:
http://en.wikipedia.org/wiki/House_of_Himiko
I wouldn't think artistry is limited to the upper classes, or that all members of the upper class would have been artistic. Look at the difference between Marlowe and Shakespeare(the best of the their time, and neither upper class) and Ben Johnson(who had every benefit of both university education and status, but whose plays didn't last).
Finally there is this:
http://en.wikipedia.org/wiki/Animal_sexuality#Homosexual_behavior