Steam is a content delivery system. It does not prevent me from adminning my own computer or 'sideloading' other programs. It doesn't tell me that I don't need -foo-, only to tell me that I do need -foo- once it's implemented there. It doesn't force me to use certain hardware. Steam doesn't even dictate what major consumer OS I should use. Steam is a content delivery system, and apart from license control for the content that I purchase through it (and only that), Steam does not mandate my user experience to behave in any particular way.

There isn't much of a wall around the Steam garden.