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Since SteamOS is Linux and they're distributing it, they have to. This doesn't mean that any of the Valve applications running on top of it will be open source. I don't expect them to be.
The question is about "SteamOS" however, not the kernel. That means that the userland might be open source as well (like android). Actually it's a must if they want people to actually port their OS to a wide range of hardware.
That being said Steam (the app) will obviously remain closed source.
Is there any reason to suspect that the SteamOS userland isn't the same (or at least very similar) to what you'd have on Ubuntu? It seems like asking for trouble to go with a completely custom userland (even if they open source it).
And right there you're going to need a sizeable chunk of X windows, and a C library, and network configuration utilities, hardware management tools (looks like this is aimed at commodity hardware + reference machines from Valve) and the guts of a web browser and Steam itself. I wouldn't be totally surprised to find coreutils or at least busybox in the default install too, for aiding and abetting system initialising (and to please the intrepid few who somehow make their way to a command line).
Sure, not contending there is userland, just wondering if there is any interesting userland that Valve develops. They won't be open sourcing steam, so the fact that they release their build of X windows that is exactly the same as upstream isn't very interesting.
One device with such a low barrier to getting started programming that kids still have access to is TI graphing calculators - I got into programming through my TI-84 back in middle school, writing quadratic equation solvers and the like , and eventually playing with graphics and simple games. I certainly wouldn't recommend that anyone specifically choose the calculator as a starting platform, but it's a great way to accidentally discover programming. And it was a great way to kill time at school for several years...
