For a long time, the argument that iOS is more profitable for developers than Android is mostly true. That argument may soon go the other way though. According to a recent Developer Economics survey performed by VisionMobile, Android developer revenue is gaining ground quickly on iOS and is nearly at parity. It's obviously worth noting that it is a remarkable achievement for iOS that they still have the lion's share of developer revenue. Android holds a majority marketshare for smartphones in the world, yet iOS still holds the lead for developer revenue.
Windows Phone is taking up a solid third place although they still have a long way to go to catch either Android or iOS. HTML5, is a strong contender and is giving chase to Microsoft for third place, while Blackberry is sucking wind in dead last.
It's also interesting to see that the revenue models are a bit different for each platform. Android makes most of its money through "in-app advertising and pay-per-download" (in that order) while iOS follows a "pay-per-download and in-app purchase" model.
You can check out more about the study at the source link below.
Source: Android closing Apple's iOS developer revenue gap | ZDNet