Irrelevant as not cross platform and this thread being about steamos.

1. The linked page (which is stats for the Unity web player) doesn't appear to cover Linux, but it does provide data for both Windows and Mac OS and break the Mac data down into finer detail than some of the other sources. Unity also provide "standalone hardware stats" (as a different tab on the very same page) which is probably more relevant to the discussion and does include Windows, Mac OS and Linux.

2. The OP specifically asked about sales "outside of Steam". Alternative information sources like the Unity stats are pretty relevant to that.

Irrelevant as not cross platform and this thread being about steamos.

The thread is not about SteamOS, it's about the Steam Operating Systems (AKA Hardware and Software) Survey.

One never knows for shure how many people uses linux or what is the purpouse they use it for. As foer me, a Linux user for some reason I don't play in Linux but I make shure that every game I buy has Linux compatibility so in the future I'm shure I can play those games.
Especially after SteamOS which promises a lot for Linux users.

That seems about right considering all other OS usage metrics around.

Even if you say "oh but most people with linux dual boot windows" and so on, maaaybe you're underestimating the value of actual linux installs by what? 20%? Lets go crazy, lets say that there are actually twice as many Linux users as the survey says (ie, the metrics are terribly wrong and all Valve employees should get a year long statistics lecture). Even then its just 2.3% of the total.

I'm guessing that if SteamOS picks up steam (pun intended) and everything goes right, you might see 5% of Linux usage... Someday... Maybe.

It's still a lot though. Say a modern AAA game sells really well, 10 million copies. Windows only game (Skyrim sold like, 8 million units the first month). Now say you could increment your potential sales by 5% by releasing it for Linux (actually its a bit more than that because its (95% of a total minus OSX usage) vs (5% of a total), but bear with me).

That's 500000 potential copies sold (and to be fair, if each pirated game is considered a lost sale, I can consider each Linux user as gained sale). Now, I won't matter much to an industry which is used to double the sales of each of their games every year, but that won't keep up forever, and that 5% someday will actually be an attractive number.

That's how I think it will be IF everything remains more or less the same, ie, not taking in account some technological revolution in between (like smartphones).

Unity also provide "standalone hardware stats"

What's that counting? The possibility to build/export for Linux is less than 2 years old? There's no native Linux Web Player nor editor. For Unity I still need to boot Windows and while developing I access various sites in store/forum etc. It only gives an idea of Mac %.

The W3Schools operating system stats tell a similar story: http://www.w3schools.com/browsers/browsers_os.asp

Here Linux is up to ~5%, which is roughly the same order of magnitude, but again, you need to be aware that these stats are going to be skewed by having a different target audience.