Today there have been quite a few sites that picked up a story from the Guardian, about Google apparently "making" 4x less money from Android than iOS - from ads. However, these headlines are quite misleading, and I don't think that at this point the difference between Google's revenue from iOS and the one from Android is that large. Here's why.
Android had 2% market share at the end of 2009, before the Droid, and 4% market share early 2010. So practically Android has only been growing for the past 2 years, and this report is accounting for the past 4 years, when Android hardly existed in the market in the first half of that period.
And even if you count 2010, and getting 30% market share by the end of 2010, this was still only for the previous quarter - not in total. By then Apple had over 100 million iPhones, about 30 million iPod Touches, and 15 million iPads. Android only had like 20-30 million subscribers by then.
Now Android has around 300 million subscribers, and growing 850,000 per day, which is twice as fast as iOS, but because of Apple's huge headstart, they still have around 350 million iOS devices. Android willl surpass it soon, but as you can see, for the main part of Android's life so far, it had a lot fewer subscribers than iOS.
The second thing, is the apps, which also matter in gaining that "total revenue". Android apps followed a similar course. At the beginning of 2010 there were like 20k apps, and Apple had like 150k, and Android gained around 150k by the end of the year, with Apple maintaining the lead with 300k in total. Now Apple has 500k vs 450k for Android.
Again, the point is, for the main part of Android's life, it also had few apps from which to gain revenue compared to iOS. This is why when the title says "generates" or "is making" it's misleading and wrong. It should be "generated" or "made". Because if we take ad revenue for the last 3 months, both platforms should generate about the same, proportionally to how many users in total both have, and how many ad-based apps are available for both app stores.