I think the reason why android doesn't have a large paid app base is due to the lack of a well designed purchasing ecosystem. People have been using(read: spend

I think the reason why android doesn't have a large paid app base is due to the lack of a well designed purchasing ecosystem. People have been using(read: spending money with) iTunes for nearly a decade. They know it and they trust it. The fact developers can be sure people will have a smooth process buying their apps encourages the best developers to use iOS as their preliminary platform. Until android has a trusted payment system that allows easy payments, developers will not spend the time to create apps for it.