You are correct, that being said there are a few "Steam Emulators" out there (of varying levels of shadiness) and Valve hasn't tried to take them down. It seems

You are correct, that being said there are a few "Steam Emulators" out there (of varying levels of shadiness) and Valve hasn't tried to take them down. It seems like they rely on "the ecosystem" as some sort of DRM over traditional almost-rootkit-level DRM implementations. i.e. initial + update distribution, achievements, redistributables, cloud saves, workshop, key management, matchmaking etc.