Speaking of gay sex scenes - if you are in the USA, check out
I Love You Phillip Morris, which opens in some theaters this weekend. (Europe and most of the rest of the world got the film last year.) Not X-rated, but R-Rated and it doesn't back off the homo sex romps. It's also funny (if you like dark twisted humor) and somewhat romantic.
...And if the whole movie is X-rated, that significantly limits the venues where it can be shown, or the places that can sell a DVD copy. Limits it, in fact, to the same places that show or distribute plain ordinary pornography.
So then you have to ask why a studio should bother with the expense of constructing an Oscar-winning storyline with well-known mainstream actors...
Two words:
Midnight Cowboy - X rated and Academy Award winner as best film of 1969 starring Dustin Hoffman and Jon Voight.
OK, I'm being cheeky - it is the only X rated Oscar for Best Picture. (Though
Last Tango in Paris with Marlon Brando was nominated in the 70's.) Your point is a good one - NC-17 or Unrated movies (there is no MPAA X rating anymore) will not be shown by most theaters. (The new Natalie Portman movie,
Black Swan faced this very dilemma. They cut some scenes so it could be R rated.)
One clarification though - NC 17 and unrated movies are shown in most big cities in theaters that specialize in presenting independent and foreign films.