This is a regular discussion that happens under every article on The Verge about some new iOS app. So far they are all flames thrown at each camp. This poster had a really good answer with good supporting facts. I thought it was worth sharing:
It’s not “gibberish” – it’s fact:
1. Android users spend less time with apps. http://www.businessinsider.com/android-users-use-apps-less-2013-6
2. Android users are less likely to pay for apps: http://phandroid.com/2013/07/19/free-apps-android-users/
3. Android users don’t buy stuff with their mobile devices as much: http://bgr.com/2013/12/02/ios-android-black-friday-online-shopping/
There is a meaningful difference, and if you’re trying to make money in the mobile world, you start with iOS.
The only thing I'll add to this is the ease of building and maintaining apps due to a more consistent group of devices with users who upgrade to new versions of the OS regularly.
Don't mistake this for developers not succeeding on Android. That is not true -- plenty of developers make a good living out of Android.