Apple is also selling app install ads in the News and Stocks apps. Tens of billions of dollars are spent on app install ads on iOS each year, so this is a very lucrative market for Apple if they can corner it (and probably necessary if they are going to achieve expected Services revenue growth in the years to come). It remains to be seen whether they’ll take another crack at the rest of the ad market, after the failure of iAd. They seem to be laying the groundwork for it.