Think about up the next generation of game developers - kids growing up right now. If they're gaming on a console and using a tablet or smart phone for their other computing need, they have no real exposure to programming, 3D modeling, audio software or any of the other things that go in to designing games. If Windows and MacOS are moving towards closed software ecosystems and a mobile interface type of simplified UI that hides everything but Twitter and a browser from the user as they both seem to be, Linux is going to have to play a larger part in gaming development in the future. The more devices and distributions tailored for different purposes and specific hardware while still allowing users to peel back the curtains to access everything available on the OS, the better off we'll all be. Kids are curious and will do what they've always done since the advent of personal computing; making cool stuff for fun and to impress people, and unless some change like this takes place, fewer and fewer people will ever be exposed to these tools.
I know my nephew got his parents to buy an iPad just so he could play Minecraft. While the mobile versions of Minecraft make it hard (impossible?) to use addons and mods, I'm sure more than a few kids have been pushed in to building a PC or getting a gaming laptop to really take advantage of what that game has to offer. It'll just take one killer app that allows people to be creative and do things on a Steambox(/Windows/MacOS/Linux) that can't be done on a closed platform to start moving these things.
And in the meantime, Valve will be taking things slow and steady like they always have and building partnerships with hardware and software developers to get SteamOS ready to take over when the inevitable decline of support from MS and Apple for desktop users pushes the hardcore audience over where the games will necessarily follow. Totally agree with the article's author, Valve isn't trying to win a war but positioning itself for a future that's seeming pretty likely if not certain. The Steam machines that are launching now are a low risk investment from everyone involved. Free advertising for Valve, and a simple rebranding of exisiting hardware for the manufacturers. The real test will be how seamlessly and well the streaming works to entice hardcore gamers into putting a HTPC or steam box in their living room, and so far we haven't seen anything there.