Apple has a top-N list for songs, albums, audiobooks, movies, tv shows, etc. on the front page of the itunes store. How is advertising questionable material in those lists any different than advertising apps with questionable content?
With iTunes, Apple is a distributor. With the app store, it's a publisher. It's reasonable to assume that most people who are likely to get angry about content in a song/app recognise and understand the difference. And perhaps many of them don't understand that Apple is merely a publisher, and don't actually create most of the apps.
Creators and publishers are (usually) considered to have more responsibility than distributors when it comes to objectionable content. I think that's an important difference for Apple's image.
