As it is now, Steam is easy to install on Ubuntu, and possible, but maybe a bit of a pain for other distros, depending on which one. It would be sad if Steam eventually only worked well on SteamOS, because of fragmentation in the graphics stack. If I wanted to choose my OS solely on the basis of what works well for gaming, I would be running Windows.

Then again maybe Intel and Valve will sort of bring some adult supervision to the distros by putting some pressure on everyone to pick one graphics stack and live with it. I'm not sure whether I think this is a good thing or not.