Richard says that their 30% would account for a tiny sliver of Apple's overall revenue, but lots of tiny slivers start to add up eventually. The problem though, is that if the cost of those slivers is to drive the developers away from the App Store, then those slivers disappear. Considering that third party apps are possibly the most important feature of the platform, it doesn't seem like a smart idea.
The 30% cut on App sales is understandable, because software generally has high margins, but it doesn't sound like the same is true for content subscriptions. Maybe it's a case of trying to keep their policy too uniform (i.e 30% on everything)?
Does anyone know where the subscription content comes from? From my understanding, the subscription content will usually come from a third party, rather than Apple's CDN, so there's no marginal cost to Apple.