Anyone who feels the 30% is "fine" - "justified" - etc..
Is there a % cut Apple could get to where you'd have a problem with it?
Would 50% be ok?
What about 70%
Taking a look at general consignment stores, which is what the App Store somewhat resembles, the typical % that the store takes is 25 - 60%. (https://www.huffingtonpost.com/uloop/this-is-how-to-make-money_b_5423617.html)
For general retail, the average is 50% (https://www.shopify.com/blog/pricing-strategies)
Based on this, 30% seems quite reasonable.