Given the ongoing security updates and years of upgrades provided to older phones, I would argue that the marginal cost of iOS is NOT zero nor anywhere close to

Given the ongoing security updates and years of upgrades provided to older phones, I would argue that the marginal cost of iOS is NOT zero nor anywhere close to it. Relatively low, sure, but one would need to figure the amortized cost of ~5–6 years of OS updates across the devices who are receiving the latest iOS this fall.