As someone who recently sold their iPad Mini to get the Nexus 7 let me share my experiences. Yes Android app store is normally cheaper, the hardware is a fraction of the cost, and the Nexus 7 is capable of everything the iPad is and then some (namely emulators for my purpose).
However, after using an iPad Mini for nearly a year I can say these things:
- The touchscreen in the Nexus 7 is not as precise as you get with a Mini.
- The OS is not as stable, mine reboots at least once a day on heavy use days.
- The apps are not as well written, one example is World Series of Poker, works perfect on iOS - won't run on android.
Just keep those things in consideration before writing off the mini for the nexus. The ecosystem is just one piece of the puzzle. I'll likely keep my Nexus for the emulators but get another iPad to replace the one I sold.