[batista]

All Android sales are potentially a double sale.

If the app-making was free. You forgot the "opportunity cost".

Android has a majority market share on phones and iPad has a (overwhelming) majority market share in tablets.

Yes, but does Android have a majority market share on apps sold? From what I have heard, I don't think so.

They just have a majority market share in phones because even people who don't care about a smart phone or apps get an Android phone for free with their contract. Whereas iPhone users are more picky in general about the phone they get, and more prone to fork out for apps. (Notice how I said "in general" --nerds are a small minority of smart phone buyers).