You're nitpicking a particularly irrelevant point the parent made in support of the overall argument, which doesn't work.
I agree that running a payments platform is not nothing. The issue is that there is zero competition in the space of iOS payments (very convenient for Apple that they get to make the rules and also benefit from them). That harms consumers because sellers will often charge more to account for Apple's 30% cut (and if Apple bans charging more on only their platform, the seller has to raise prices for everyone, which hurts their non-iOS user base). An alternative payments processor might charge 20% or 10% or even less. Healthy competition in that space would benefit consumers, while forcing Apple to charge a fee more in line with the actual cost of what they provide.
(There are certainly downsides; Apple has done a lot of work to ensure the security and privacy of their payments solution, and other processors may not do as good a job. And without restrictions, it's the seller who decides what processors to support, not the buyer, so the buyer doesn't get to -- for example -- choose to pay a little more to keep their information in Apple's care.)
Perhaps a good compromise would be for Apple to require that apps support Apple's in-app payment system, but allow other payment methods in addition, and also allow sellers to charge more to users who use Apple's system. If customers don't value whatever Apple is providing for the extra fee, Apple will be incentivized to charge less.
> Possibly charging app developers directly for access to the app store.
They already do this, via the yearly developer fee.