If I lease space to you on a profit sharing based model (i.e. you don't have to pay any standard rent but you need to forward 20% of what you make in lieu of rent to use the space) and you start giving product away to customers for "free" but then force them to pay the actual price under the table then you're committing fraud. Whether you think 30% of transaction value is a fair price or not for the costs of running an AppStore (I don't think so - it's ridiculously high proportion-wise) that's the agreement. Apple comes down hard on people who run microtransactions via alternate payment methods in application on their platform and yet that's exactly what they're doing in the Play Store - it is something that Google allows, but it would violate Apple's ToS.

There is no prohibition to allowing subscriptions outside of the App Store - even at a lower price. Apple is saying you must also allow subscriptions in the store. Whether you agree or not is different.