I do think it's all kinds of interesting that Infinity Ward is making this kind of noise about the Piston. If Microsoft keeps dynamiting its brand like it's been doing, well ... it's like I've said before, I think there's justifiable reason to be hopeful. Personally, I'd be all giggly if I could get Half-Life 2 sometime soon.
On-topic: I don't think the amount of Linux users will increase in near future this fast. The majority of people interested in Linux gaming are probably using Steam until now, so the future increases for Linux share will be much less. Current 2 % is pretty well on line with web OS statistics too (although they aren't very reliable).
However, things might change quickly if Valve or some other company decides to release some big AAA game exclusively for Linux first. Half-Life 3, anyone?