I don't think that the Oil situation is comparable to the Open Standard PC. Everyone can decide to buy the next game on a different platform. You are not really locked to the Steam eco system. If your nation is based on Oil, then you are screwed. That is hugely different situation.
No, Steam is not a real monopoly. Steam also does not abuse the monopoly like Google does with their positioning and control of Android. That's a real monopoly. And Nintendo is a monopoly too, regardless how you frame it.