Ben Thompson:

“While Facebook’s ad network is, I’m guessing, broader than just app installs, the reality is that app installs dominate Facebook’s mobile revenue as well. And, the primary types of apps that advertise for installs are free-to-play games, looking for the specific customer type who will potentially spend hundreds of dollars on in-app purchases.

This, then, raises a frightening specter for both Twitter and Facebook: they are indirectly exposed to any changes Apple or Google may make in their policy with regards to in-app purchases”

Fascinating point.