Neither. http://store.steampowered.com/sale/linux_release/ is currently showing off their Linux sale, you can page through the games they are selling and become less naive/unaware of what is out there. It's no Windows, but there are some games.
One of them is Half-Life. It's fifteen years old.
http://store.steampowered.com/app/70/?snr=1_614_615_linuxrel...
That's a great question.
Obviously, I am simplifying a complicated legal system with my reply. I am not a lawyer, but I have studied open source licensing.
With some exceptions, the Linux ecosystem does not eclipse for-profit software. You are free to run closed source software within an open ecosystem.
With that said, I personally develop and sell open source games. Linux is a first-class citizen in my market. I find that the person who makes the decision to run Linux as their main OS is the same type of person that will avoid a purchase of software that is closed source. In that case, the barrier is the mentality of your users rather than licensing restrictions.
I'm completely unaware of games, or any software, that is sold specifically for Linux (sold, being the keyword here). I've never installed Linux and purchased software for it.
So, my question, does the Open Source ecosystem for Linux simply eclipse the for-profit software, or are there special licensing requirements that are difficult to comply with?