Revenue for music apps grew 77% in 2013, year-over-year, according a the App Annie Index: 2013 Retrospective report. The report studied income derived from both free and paid apps. In the free category, in-app purchases applied — as with Pandora, Rdio, Deezer, and Slacker, each of which falls into the top 10 revenue-gaining music apps. Advertising revenue was not measured. So the growth of music-service app revenue is accounted to in-app upgrades to subscription service.
Interestingly, in a confirmation of Apple’s assertions, iOS revenue growth substantially out paced Android revenue growth. In some of its live events, Apple has touted the money-making aspect of its iOS app store.