Everyone is forgetting that currently Steam has a pretty high hardware requirement if you want good fps(the games listed i mean), and that The games aren't really all that stable atm(mainly referring to TF2 here, since its the official give out, but you can argue about the others too).
The stats reflect just that.
Even if we realize that Linux isn't going to pop up into 10% like magic, as many would wish, the truth is that, it would have been a lot higher given different circumstances. Its just BETA after all.
Cheers