Steam users are not average PC users. Believe it or not but gamers are actually just a small percentage of PC users. Most people don't game on their PC, if they even game at all. I'm talking of course about non-browser games.
A good example for this is that AMD actually beats NVidia in graphics market share in the Firefox survey. Of course, Intel beats them both, which is clearly a result of laptops and low-end form factors.
Similarly, just look at the absolute dominance of 2-core systems on the Firefox survey!
