iOS dev tools may be cheap. But that's not point. Apple has invested billions into that ecosystem. And to foster adoption, Apple's licensing model allowed for "free" software. But that was funded by the revenue collected from non-free iOS apps.
1990s-era Windows was a sort-of monopoly -- MS had a monopoly on Windows, and Windows ran on the substantial majority of PCs, and PCs were much of the market. But users could also get a Mac or one of several Unix-ish machines or an OS/2 machine or a BeOS machine, etc. So MS's actual monopoly was on platform that developers needed to target to make software to run on Windows machines.
Right now, Apple has a monopoly on the software running on iPhones and iPads and a near-but-not-complete monopoly on software running on laptops and desktops and Mac Minis. And there are plenty of users of various Android phones and even a handful of devices that are neither iOS nor Android.
So what's the difference? Apple wants to take a cut of gross sales of software targeting iOS, even in cases where Apple is uninvolved in the distribution of that software, and even when that software actually targets a platform-agnostic system and that system knows how to target iOS. Microsoft did not.
Different from who? What company in the 1980’s or 1990’s did what apple is doing now?
This is a strange concept, especially in historical context. Windows, for example, was always free to develop on unless you wanted to use MS’s tooling, in which case you could buy in a la carte or subscribe to MSDN. The owner of the device had a license to the technology and MS’s stack, and the developers licensed the developer tools if they chose to do so.
Even on iOS, the dev tools are cheap, and the device owner holds an iOS license. And the charge for distributing software is $0 — there is no charge for distributing software.
So what Apple really seems to be charging for the is permission to charge money for iOS apps. And I think I’m with the EU here — Apple is gatekeeping and is charging something entirely unrelated to Apple’s costs.