Our app is #8 in our category in the App Store and #13 in for the category in the Android Marketplace. It is free and has no advertisements; only available in US / Canada markets for both. We only get about ~1250 downloads a day on Android and about ~3500 downloads a day on iOS.
With that skew in raw downloads combined with a variance of stereotypical buying habits on each platform it is easy to see a way where iOS revenues could outweigh Android revenues by a lot.
From our standpoint, at our scale, advertisements are almost worthless to the amount it would hurt our brand. No agency, in Google itself, has shown us revenue predictions that make our mouth water. We have also experimented with a few direct placements (heavily target to our audience, and we did the design work of the advertisements ourselves) but will likely not continue with that in the future because of how bad they perform.