Apple is sitting on a $150 billion warchest of cash. I'm guessing that some of that comes from what they're charging above these non-negligible costs. They don't have to run a charity, but they're making fucktons of money between all their products so it's hard to see their 30% cut as anything other than extortion.

That cost is negligible relative to the tens of billions they rake in via fees charged to iOS app developers. You could do the math, but I'd guess it most likely wouldn't even exceed $10 million a year.