Most of the highest-grossing applications are now free-to-play and monetize primarily through the sale of in-app purchases. You can see this in the iOS charts where 14 of the top 25 grossing apps are currently free and on Android where 19 of the top 25 grossing are free as well.
Inside Mobile Apps breaks down the Piper Jaffray report on mobile application revenue by platform that suggested Android represented only 7% of iOS app revenue. As always, IMA is on the money in their analysis but the one important thing to note is the category of apps that monetize through in-app purchase. Sure, this strategy is employed by a majority of the top-grossing apps, but those apps are all games, specifically social games. Other categories of apps, including games that lack a social component, typically need to find other ways to monetize.
(h/t eCPM Blog)
