Playing devil's advocate here, if Apple charged everyone 30% this would mean iOS wouldn't have
-Microsoft
-Netflix
-Amazon
-Spotify
-Google
-Hulu
-HBO
These companies pay less than 30% but would developers have an iOS to develop for with an audience worth developing for if these apps looked elsewhere? iOS loses MS Office and Netflix, there goes half of iOS users and therefore developers have no reason to make apps for it and Apple begins a 10 year downward spiral of iOS dying completely.
By making these deals, Apple keeps those companies in the store, enriching the username and making iOS happen for millions of indie developers stuck paying 30%.
I would prefer Apple just drop it to 10% across the board for all developers and be done with it.