I highly doubt the richest 1 billion have anything at all to do with the majority of Android phone purchases. Countries like Nigeria (140,000,000 people) and Kenya (40,000,000 people) are starting to see their populations going from no-computers to everybody-has-a-smartphone. Most people there may never own a PC but will move straight to cheap, open source smartphones.
I would bet that Android's growth numbers are a majority of new users and a minority of returning users. The platform's only been popular for a single "update cycle" anyhow. 3G networks are popping up in the poorest parts of the world and people are buying phones there.