Steam has a native Linux client.
Not just Steam, but one of the most wildly popular games among kids, Minecraft, plays on Linux without a hiccup, assuming you’re okay with installing Java on your Nix desktop.
I LOVE my Ubuntu desktop. I think one of their bigger challenges, one I’m dealing with right now, is their LTS (Long-term Support) distros (i.e. Ubuntu 12.04) aren’t as “long-term” as say, Microsoft’s Windows. I’m having to upgrade all of my 12.04 servers to 14, and while it’s a pretty painless upgrade, there are some features that are tweaked just enough to make troubleshooting difficult on some products.
If they could come out with a universally stable OS that’s patched and updated for, say 2 or more years, they’ll have something that’s commercially viable.