There is a big, obvious difference between the app stores and the music business: The number and transparency of middlemen.

If you want to know how much money an artist makes from selling a CD in a supermarket, you can find a large number of handwavy blog posts, but the conclusion is consistently "probably not a lot, but depends on what they could negotiate".

If you want to know what an app developer makes from selling a $0.99 app? The answer is $0.70.

I think that makes a lot of difference in trust in the channel from both sides of the table.