Beg to differ:

At least as of this posting, the Linux users are paying around twice as much as the Windows users and about 50% more than Mac users.

As a side note, I've heard good things about most of these games, and I can say that the one I've played, Penumbra: Overture, is very good, especially for an indie. When I get home I'm planning to look into doing my part to push that Linux average higher.