Analytics firm Distimo has published its end-of-year report on the major app stores, and it includes figures showing why so many developers remain focused on Apple’s iOS. The report compares revenues generated by the 200 Top Grossing apps on the various stores in the US, and finds that they make four times the revenue on iPhone as on Android. In fact, even the 200 Top Grossing apps on iPad make twice the revenue as the Top 200 on Android. The report also highlights the popularity of freemium business models, with half of the 200 Top Grossing apps for iPhone being freemium, and 65% of the Top 200 Android apps. Distimo has also produced a chart of the top 10 apps across all mobile platforms. No music apps make it in – here’s the top 10: Angry Birds, Facebook, Skype, Angry Birds Rio, Google Maps, iBooks, Angry Birds Seasons, Fruit Ninja, Talking Tom Cat and Twitter.