Don't have to support every distro,just the major ones like Ubuntu through Steam and the Linux community will figure out the rest.
Do you mean current AAA games? Because there are plenty of older titles like the Borderlands series, Civ 5,Dota 2,indie games which run on Linux through Steam.I know it's a joke at this point, but nobody plays games on a Linux machine...
People who play games on Linux, do so because they have a political knife to sharpen against Microsoft and little else, thus many of those who ask for Linux support can't even point to a Linux distribution that will run existing games with Linux ports of of the box. Even Steam appears to have abandoned it's SteamOS based on Debian, with more than half of the issues still open.
I think Windows 7,8.1 and 10 are pretty good OSes. However, my experience with Linux has been better in terms of leanness,system stability and control.
Again that's fine, they don't have to test on every distro.Go with Debian/Ubuntu.Steam is easily installed in popular distros through their respective software centres/package managers. It really is not "jumping through a lot of hoops" from that point to get it working on others for the Linux community.That's why developers don't take Linux development as a first-class citizen seriously. Some software developers release a "Linux" version that only works on one flavor of Linux, that which Steam supports (Debian) and if you don't know how to launch Steam on Linux, you aren't going to get those games on any other flavor without jumping through a lot of hoops.
...since the developers can not test on every distribution or fork of that distribution and may only test on their one linux machine in the office.
I don't think SE will ever do a native Linux client simply because of OS market share but it would be a nice gesture and 1 less reason to keep Windows.