1. Why Apple?

Looking through a few links, I found some interesting statistics:

While the number of Android users outweigh those of iOS, the iOS developers are able to monetize their applications far better. If the number of apps made by an average developer is pegged at five, then the revenues earned by an iOS developer would be five times that of an Android developer.

How much do iOS App Developers usually make?

Dividing 5000 million by 235 thousand developers, an average developer makes roughly 21 thousand USD

How many apps does each iOS developer make?

Dividing 1250 thousand by 235 thousand iOS developers, an average iOS developer makes  5.3 apps.

How much money does each app rake in for an iOS developer?

Dividing 21 thousand USD by 5.3 apps suggests that an average iOS developer earns roughly 4 thousand USD on each app.

What are the major sources of income for an average iOS app?

It seems that the average price of an iOS app is 0.19 USD compared to 0.06 USD for an android app. Roughly one third iOS apps generate income by in-app advertising. Another one-third generate income by pay per download model.

What is the pay per download model?

Each time you download an app, you will be taken to a third party site which either helps the user unlock the product (your app) after he/she has answered a survey('after download'), or just before he/she is about to download the app (i.e. the files haven't been transferred from the server to the user's smart phone)

Considering that an iOS app requires 19 cents for download, how much of the revenue per app comes just from download?

Dividing 50 billion downloads by 1250 thousand apps suggests that each app is downloaded 40000 times. Multiplying 40000 by 19 cents gives us 7600 USD on mere downloading fees per app. This is more than the 4000 USD revenue on an app, so the 19 cents figure is probably wrong.

Sources

1. https://fueled.com/blog/why-do-iphone-users-spend-more-on-apps-than-android-users/
2. http://www.forbes.com/sites/tristanlouis/2013/08/10/how-much-do-average-apps-make/
3. http://www.kantarworldpanel.com/global/smartphone-os-market-share/