To my knowledge most developers aren't exactly earning a mint from either platform. There are success stories on each platform, although as the iPhone at one time had more users it seemed only logical to go for that market.

Android is now at a point where the average user couldn't care less about OS having open-source aspects. The reason few people buy apps for Android is because while there are a lot of apps most of them are awful or have free alternatives. This is what separates the iPhone experience from the Android experience, and in my mind this is why people don't spend big on Android, and why people would if the right app came along.