Your point about backwards compatibility is the key one, I think. Windows allows space for experimentation by accidental virtue of the side effect of being so good at back compatibility.

If Windows didn't have to support a gigantic universe of old-yet-critical software, Microsoft would have radically reduced the API and feature surface and Windows would be as locked down as MacOS is.

If you can play around on Windows today you probably should be thanking some person who wrote a VB5 program to control a nuclear reactor in 1996 and insisted that it talk to COM1: (gulp).

> If Windows didn't have to support a gigantic universe of old-yet-critical software

Interest point, but not exact.

MS have close to monopoly state and is very close to formal margins, where regulators must issue regulative measures.

As I know, nearly all companies achieved so huge share of US market, got warning from regulators, and most immediately hit brakes to limit their share and avoid measures. Examples from past are IBM, Commodore/Atari, etc.

But what interest, using some obvious things, like just strip API to limit share, considered by regulators as offense, so subject must not do direct things to limit his product, and only could slow innovations.