It's interesting how many of the same arguments used by the Apple Defence Force (costs for providing SDKs, tools, infrastructure, etc.) also apply to Epic's Unreal Engine and related software. Epic's model there is that anyone can freely use it at zero charge and no strings attached, until one's game or software developed using Unreal Engine generates a certain amount of revenue (recently upped to about $1M, I believe).
This way independent, small-time developers can do whatever with zero risk or costs, and by the time Epic comes around with the first invoice if one's game turns out to be a sleeper hit, one would presumably be raking in enough dough that the whopping 5% royalties Epic asks at that point would barely register.
In that regard, Apple's 30% fee for even the smallest developer seems somewhat greedy, especially when one realises that it's not a flat 30% fee, but it are often the bigger parties on the App Store (like Amazon) who are paying significantly less.
Essentially it appears that in the case of Epic, it are the big players who are funding the party for the smaller players, whereas Apple seems to be more into flogging the smaller developers for cash, to entice bigger players to please not avoid publishing for iOS. Which feels rather... shady.
Personally, I see smartphones as more or less closed & locked-down platforms (even Android), and the Google & Apple stores as pointless treadmills if one's goal is to make money, but that still doesn't give either Google or Apple to act like greedy leeches.