I'm willing to defend Apple because I'm tired of disingenuous arguments from either parties with self-interest or FOSS advocates who have some ideological opposition to Apple's closed nature (and have since the beginning of the App Store and decades before that with Macs).
Apple's customers don't care about the margin structure or costs of app developers. The App Store has massively increased both the supply and demand for apps, and it has actually led to a decline in prices for software. Everyone knows this because they've been complaining about how they can't charge as much for apps as they did in the packaged software days.