Competition and Ecosystem Economics - Good read
I found this article from Vision Mobile blog, which does great Infographics and articles on the mobile market. The specifically mentioned Apple in the following exert but said the Google Android ecosystem works in similar fashion.
Long story short I find this is the main reason why Windows Phone and Blackberry may have issues pushing their devices as Apple and Google have spent years building "lock-in" for the iOS and Android ecosystems and Microsoft and RIM are still trying to define what their ecosystem is. This is not really Android specific, but it is a great read and insight into the economics behind mobile ecosystems.
Ecosystem economics are driven by network effects and lock-in. iPhone apps attract Apple users, who in turn attract more developers, who make more apps, which attract even more users, and so on. This network effect between developers and users drives the explosive growth of the iOS platform. Lock-in creates natural “walled gardens,” as users develop habits around apps, while developers are locked-in by high switching costs created by their investments into the platform.