While I think games and such have a right to not be free, the fact it is the most gigantic market out there at present. If they continue to be locked to Windows and Mac, you'll have a monopoly. Today, we at least have the luck of installing what we want on our Linux and Macs, but in the future the giants want it all to go through their stores.
The sooner that Linux becomes at least a casual-to-frequent gamer platform, the better it is for the entire market, regardless of the closed status of the games themselves. Microsoft understood it very well once upon a time: an OS is useful without apps. And the more of a users needs can be catered to, the more successful the OS will be.