One of the things developers often consider when comparing the opportunities for revenue in Apple's App store and Google's App Market is that in the latter case there projects could not be monetized using in-app purchases. The issue even lead some developers like, Spacetime Studios of Pocket Legends fame, to come up with their own options for providing users with a way to purchase digital items from within their app. Now Google has finally released in app purchasing to their market place (cue thunderous applause from the developers here).
Developers have enjoyed this option on IOS for three years now (2009) and it has proven to be extraordinarily lucrative.
Though advertising has been a major way for dev's to monetize their apps on the Android Platform (just ask Rovio), in-app purchases has driven revenues through the roof on IOS and has made more money overall for developers.
This feature has been long overdue and it makes me very happy to think that the platform will now bw more appetizing for developers. Disney's Tap Tap Revenge, ComiXology's Comics and Glu Mobile's WSOP Hold'em Legend are three apps that feature in app billing right now. Now that Google has the revenue stream flowing in the developers direction Android is that much more viable and its about time.