Another curious statistic: according to the sales numbers on http://www.humblebundle.com/, Linux users on average pay more ($12.50) for the choose-your-price bundle than Mac ($9.99) or Windows ($7.98) users.
I would guess that this is either related to user enthusiasm for more professionally developed games (explaining why Windows users aren't as excited), or a desire to support the creation of cool stuff and be part of a community around it.
Additionally (ceteris parabus) a Linux user would be richer as they have not spent money on an OS (except the odd RHEL user). However I doubt this makes a statistical difference.
But you left out the counter-balance: far more revenue is generated from Mac and Windows users in total. So while Linux users are willing to pay more, there's far less of them willing to pay at all.
Far more revenue is generated from Windows. Mac is a very distant second. The camembert says something like For each 6$ from windows users, there are 2$ from mac users and 1$ from linux users...
