That is an interesting question. I've also read about other counter-intuitive revenue statistics. Apple's share of hardware revenues is way higher than its sha

That is an interesting question. I've also read about other counter-intuitive revenue statistics. Apple's share of hardware revenues is way higher than its share of unit sales. And I've read that for many app makers, their revenues on iOS is higher than their revenues on Android, despite there being a larger number of Android units in the market. If the latter claim is true, it could be that iOS users as a whole spend more money than Android users as a whole. That could filter through to Google in the form of iOS users being more inclined to click on higher-value ads. Note: The above is speculative, I recall reading these claims on Daring Fireball, but that is not evidence.