Slightly more charitably, perhaps Apple recognized that for many app manufacturers who offer both paid and free versions of an app, Apple already has an existin

Slightly more charitably, perhaps Apple recognized that for many app manufacturers who offer both paid and free versions of an app, Apple already has an existing financial relationship with them, so allowing Apple to handle the ad payments from the free version of the app is going to be more convenient. Of course, there's no reason it can't be both.