According to some research by Gene Munster/Piper Jaffray, of the 4 billion app downloads on iPhones, iPods and iPads, 81% are free downloads, and the other 19% average a cost of $1.49.
Doing more math, such numbers imply that Apple has pocketed $428 million from apps since the launch of their App Store—about 29-cents per app—while shelling out about $81 million to distribute said apps.
It sounds like a lot of money, until you realize it represents just 1% of the $33.7 billion in Apple's gross profit over the same period of time.
Of course, there are a few points to note:
1. Apps sell iPhones, so they indirectly produce much more profit
2. "Free" apps that included advertising were not separated in any special way
3. iAds are the clear response to this free app bundled with advertising model, meaning...
4. Apple has long seen this app revenue discrepancy, and they want a bigger piece [AppleInsider]