Openxcell has a useful article on mobile app user retention. That is, the number of users who continue to use an app. They describe how gamification, rewarding users and giving them a sense of achievement can make apps more compelling and improve retention.
While retention rates were similar across Android and iOS last year, 2014 has seen Android surpass iOS…
Openxcell doesn’t provide any explanation why retention is so much better on Android. I doubt it’s because Android developers are better at retention. I suspect it’s to do with the difference in the types of apps across iOS and Android.
Openxcell also provides a list of analytics tools that can be used to measure app retention.