And how is Steam not a closed system? It is, but currently relies on an specific level of openness in a platform to operate. Microsoft and Apple are vertical

And how is Steam not a closed system? It is, but currently relies on an specific level of openness in a platform to operate. Microsoft and Apple are vertical integrators. They don't. So when the parent said "it seems that Microsoft is fast headed to a closed platform" they were referring to specific aspect(s) of the openness of the platform (Windows). Not saying that Steam was a free-for-all.