|This chart has all the data...see the original here.|
The numbers work out to about $8500 per publisher per year, which isn't a whole lot. Of course, that's averaging; the publisher with big hits make hundreds of thousands or millions, and many just make a few hundred dollars.
Games are more lucrative than non-game apps, and that's a good thing for game developers. But it underscores just how difficult it is to make money with an iOS game... or any smartphone game, for that matter. Developers need to be aware of the facts before charging into an expensive development process.