Amy beat me to this, but there was a great discussion last week on Idolator about Disney's control of the music industry, at least as it pertains to tweens. The thing I took from the article and subsequent was just one more confirmation that Disney's success lies in its vertically-integrated structure, of which Carnegie Steel was one of the first examples more than a century ago. From the grooming of artists on their television shows to the molding of albums by the music side, and back to the TV and Radio Disney side for constant promotion, it's no wonder they dominate this industry. (The only wonder is why nobody else has been able to copy their success.)
In fact, if you read this interview with Radio Disney's Senior Vice President Jill Casagrande, you'll see lots of mentions of artists like the Jonas Brothers, Hillary Duff, or Miley Cyrus. What you won't see is lots of mentions of artists who aren't in the Disney stable.
Disney does a good job of picking talented artists, especially in the sub-tween demographic -- they're distributing They Might Be Giants and Ralph's World, after all. But it is striking exactly how much big business has capitulated to Disney. They've left the field wide open to Disney -- how many more High School Musicals will it take before somebody else steps up?