There is an elephant in the room here, and it's why so many content providers seem just so annoyed.

Regardless of whether this is 'fair' for Apple to do or not, many content providers simply /can't/ give Apple (or any third party) 30% of their revenue - even just for for subscriptions sold through iOS apps - and still make a profit. There's just not enough margin in what they're selling. Since Apple is demanding that the prices in-app be the same as outside the app, these providers have two choices: raise prices for everyone to subsidise the iOS-purchased subscriptions, or don't offer an iOS app at all.

This is a big change to the status quo.