I still think John Siracusa's description of this on ATP was excellent. To paraphrase- its ok to for Apple to charge something , the argument is over how much. And with this type of service, and without strong government intervention, its really market-dependent. Game platforms have very similar percentage cuts (Apple probably copied that from the get-go). However, game platforms do a much better job of managing their relationship with their developers, generally making them feel that the value proposition is worth it on all sides. Apple instead adopted a very top-down attitude, and allowed this (perhaps fair) impression to develop that Apple was taking more than they are owed. Without correcting course, the next step is government intervention, which no one wants. Its probably too late, but Apple should have a long time ago recognized this and worked to make the App Store terms and conditions work better for everyone.
Muddying the waters though are companies like Epic, who do stuff like this themselves, but still made a very public argument that Apple is stealing from them.
Ultimately, I think the payment processing is small beans. I'm really hoping that Apple could reach a good compromise to avoid more terrible legislation. There are some of us who like the idea of a more restrictive environment for a device like a phone. I really do fear that if there are "alternative" app stores, big players like Facebook or employers will force us to use them, never again allowing me to have the device I wanted that was more restrictive.