These two facts are not necessarily in contradiction. At this moment in the current Humble bundle, the average price paid by Linux and Mac users is significantly higher than the average price paid by Windows users, but the total income from Windows is still way higher than the income from Linux and Mac combined, just because of the raw numbers of users.
It looks to me like there are some Linux users who don't mind buying games (and do not mind paying premium for that), but the majority is not interested in buying games at all, regardless of the price.
Moreover, my own experience with buying games is that (digital distribution aside) it was practically impossible to get Linux versions of games (well, at least in Czech rep., where I used to live). And if there was a Linux version at all, using it meant buying a box with the Windows version and the patching it. So, even though I use Linux for work, I used to play games almost exclusively in Windows (and then on XBox, which made things even easier).
It looks to me like there are some Linux users who don't mind buying games (and do not mind paying premium for that), but the majority is not interested in buying games at all, regardless of the price.
Moreover, my own experience with buying games is that (digital distribution aside) it was practically impossible to get Linux versions of games (well, at least in Czech rep., where I used to live). And if there was a Linux version at all, using it meant buying a box with the Windows version and the patching it. So, even though I use Linux for work, I used to play games almost exclusively in Windows (and then on XBox, which made things even easier).