Indeed. They are not measuring total revenue, but "efficiency". This doesn't show that the developers make more from Amazon app store than they make from the Pl

Indeed. They are not measuring total revenue, but "efficiency". This doesn't show that the developers make more from Amazon app store than they make from the Play Store. That would be very hard to believe, considering there are around 60 times more "Android" users than Kindle Fire users. But it does measure app store "efficiency" in relation to the iTunes store - with the Play Store being 4x less efficient (believe it or not, it used to be 50x less efficient in the past) than the iTunes store, and the Amazon store being only 11% less efficient. Google's problem is their lack of a "popular payment method". They slacked for years with Google Checkout, and now when they need it most for Android, (almost) nobody uses it. This brings huge friction in the buying process for most Android users. Compare this to iTunes and the Amazon app store, where pretty much anyone in the Apple ecosystem had an iTunes account that they could already use to pay for stuff, and the same goes for Amazon/Kindle Fire users. There are probably other factors which lower the Play Store monetization efficiency, too, but I believe that's the biggest one by far - so if Google wants to help developers make as much money from Android as they do from iOS, they need to either make Google Checkout very popular for other purposes/services fast, or they need to allow Paypal as a default payment method.