> can you get a new Mac laptop or desktop for under $800?
For low values of desktop and ignoring hackintoshes, yes: http://store.apple.com/us/browse/home/shop_mac/family/mac_mi...
> For Linux users... I don't know. I would posit that Linux users tend to be more educated than the average person (based on personal experience), and that more education correlates with more income (this I can actually cite: http://www.bls.gov/emp/ep_chart_001.htm).
I'd think more of "games starved" and "want to entice game developers".
I would suggest that Windows users cover the entire range of users, including a lot of minors. It's the most accessible and prevalent OS, and therefore people with the least amount of money are most likely to be using Windows.
For Mac users: Macs are without a doubt more expensive than WinPCs. Serious question: can you get a new Mac laptop or desktop for under $800? These people have more money to spend on computers and more money to spend in general.
For Linux users... I don't know. I would posit that Linux users tend to be more educated than the average person (based on personal experience), and that more education correlates with more income (this I can actually cite: http://www.bls.gov/emp/ep_chart_001.htm). I know, a stretch, but I to me they are reasonable arguments, if lacking in evidence.