What? Your math seems wrong.

The registration fee is $99, Apple has paid out $4 billion as of February this year, and there are ~.25 million registered iOS developers in US, let's be generous and say there are 1M registered developers worldwide. It still averages out $4K pay out per registered developer.

How can you use the $12 per iOS device app revenue to extrapolate average developers' income is totally beyond me.