And the sad fact is, that as of today, Windows 8 under steam outnumbers *all* versions of Mac OS all together. You can bet that the desktop distribution to Mac is higher than Linux, so what is the point here?
Valve is caught with a problem, they are trying desperately to stay relevant in an era where XBox is actually really good, and while the integration into Windows 8 leaves much to be desired, you now give companies a huge benefit in added revenue via XBox points and Xbox Achievements (which points can unlock certain things). Simply stated, developers and publishers make more money through the Xbox channels than they do anywhere else.
I know the idea of Linux gaming is great on /. but let's face the bad news; only if the community takes on the challenge of porting games (ala Wine or something), will it ever be bothered to be played. And even then, every Linux "gamer" will keep a Windows partition because all games will come to Windows, and only some will come to Linux -- and that's in an ideal world. So if publishers/developers know this, what's the point in adding Linux support in? The games won't play as well, they will lose added revenue via Xbox points/achievements, and they will make a few nerds happy.
Sorry to say but getting a Humble Bundle developer to push the idea that Steam on Linux will be "moderately successful" to "wildly successful" is idiotic and naive. Next time show an interview from a big name publisher and let the entire interview be three minutes of laughing.