I'm just saying it's one factor out of a lot of factors. They aren't playing blind so they still get some of the neat graphics, even if it isn't shiny. Then their is gameplay, audio, challenge, replayability. There are too many things to list. So playing games as a hobby isn't only about graphics, and graphics are actually only a small party, especially to them. I on the other hand sometimes just play crysis to stare at the pretty images =P.
As for the first point. I haven't tried DoW2 yet and have no intentions of playing mass effect on pc, but left4dead runs flawlessly with high settings on my macbook.
Besides the macbook air, the macbook is their (second) LOWEST end system. So that's basically saying apple doesn't sell cheaper, lower end products and therefor every mac can run these games well.(which sucks for anyone looking for a cheaper product who wants mac os x.)
[fyi I say second lowest, because it is beaten by the lowest end mac mini, which only has 1gb of memory. That is the only difference. If someone didn't like that they could install 2 or 4gbs... I know I definately would. With the mac mini plus 4gb of memory it would put a person back $600 + $100 = $700]