For every 10 apps that developers build, roughly 7 are for iOS. While Google made some gains in Q1 2012, edging up to over 30% for the first time in a year, we believe this is largely due to seasonality, as Apple traditionally experiences a spike in developer support leading up to the holiday season. Apple’s business has more observable seasonality.
This actually makes sense because Apple has more users and a better ecosystem, giving developers a far greater chance of making money off their creations. A few iOS developers have begun to make apps for Android lately, though. Instapaper is an example.