MPAA Bias Against Indie Films?

Timothy Noah with the case of bias by the MPAA when doling out harsher ratings for indie movies:

For some time, critics like Kirby Dick (director of the anti-MPAA documentary This Film Is Not Yet Rated) have argued that movie ratings are biased in favor of Hollywood insiders. Sex and violence in studio-made films, it's been said, are given greater leeway than sex and violence in the latest sensation from Sundance. The most recent puzzler was the NC-17 rating initially given Blue Valentine, distributed by the Weinstein Co., for an emotionally intense but emphatically unerotic sex scene that wasn't remotely explicit. (The scene is so achingly sad that its only likely effect on teenage carnality will be to discourage it.) In that instance, the MPAA came to its senses and reversed its decision, assigning the movie an R rating. Would the MPAA have ever assigned its most punitive rating to the film had it been made by a major studio? It didn't back in 1973 when it gave an R rating to Blume in Love, a Warner Bros. release that included a scene that differed from Blue Valentine's mainly in that the husband rapes his (ex-)wife.