Except that those numbers are incredibly weak when compared with the "mainstream" game channels.
When I checked, there were $488k in 82k sales. That's for 4 titles and a charity. Assuming a 100% revenue push from customer to developer (an impossibility), that means their average of $5.95 per sale gets split into 4 companies equating to almost $1.50 per sale, per company.
So we've got $122,000 total possible revenue without any removal of revenue hitting the developer. If you're a one or a two man independent development team, Congrats, you get to (possibly) pay your bills. If you're a 3 or a 4 man team, you're still working a second job. If you're at all bigger, you'll be shutting down unless you have another source of revenue for your game.
Out of those 82,000 sales, less than 25% are linux sales, but even going with 25%, that means 20,500 people specifically bought the Linux version.
Now, not all of the users on Steam have paid $5.95, but I'm willing to be a vast majority have. As I type this there are 4.1 million users on Steam and the vast majority of them are going to be Windows.
So honestly it really isn't hard to argue that there's no market. 20,500 people is great for an interest group, not for a global market.