1. Are they including revenue based on advertising on apps in the android market and 2. I do not think as many app sellers are trying to leverage Android to make money.
To defend these two statements we look at Angry Birds .. which is easily the most popular phone game app to date even before it was free on android. Why did they put Angry Birds on the market for free, of all the game developers they had the market awareness and draw to actually sell it and make a profit, but instead they chose to give it away free w/ advertising. So the question is, has that advertising paid more than they would have made selling the game for $1.
Don't get me wrong, the android market was not designed as nicely, and until very recently you could only browse via the phone (now you can use market.android.com). I think its a combination of two things ...
1. Some of the top game developers for iOS (apple) have not yet moved into the android market. Game sales make up 70% of Apples app sales. Until more higher quality game developers bring their products to market on Android, android sales will not grow as fast.
2. Game developers on android need to stop giving their stuff away for free w/ advertising OR they need to get statistics on how much revenue the android developers are making from advertising vehicles as this might change the reported app market revenue numbers.
3. Lastly ... google doesn't care if they make as much money on app sales as Apple. Googles primary goal with Android is to have more and more people using their technology and seeing their Ads. Google makes money on Ads. So if developers give away free apps on google and those apps have google ads in them, Google is making money via the method it wants to make money. It would be interesting how to see how much money Google is making in this way.