It's free in beer, and free as in speech. The developer experience is much better on Linux; doing something like running all your video assets through a converter in parallel is a one-line shell script on Linux [1], but a hundred-line Python script on Windows. Subjectively, on Linux filesystems seem to be faster and overall memory usage seems to be smaller.
Seriously, a long time hardcore unix guy doesn't see the benefits of Linux over Windows?
Nope. Linux barely even resembles unix at this point, as I mentioned. That one line shell script is also a one line shell script on windows, install cygwin or learn powershell. I find the developer experience on linux to be terrible, I do my development on openbsd running in virtualbox regardless of whether I am running windows or linux.
Having said that, I do still find Linux to be a much more stable and high performance platform. One of the reasons I dread dual-booting is that it takes about 5-10 minutes after booting for my Windows installation to be properly responsive to commands. I know I can re-format, but I don't feel I should have to. I've been running the same Arch install for longer than I have Win 7 and haven't had to resort to massively drastic tactics like that yet.
I guess it all comes down to lowering the barriers to entry. Ultimately the mass-market will use what is installed on their computer when they buy it. This gives the major manufacturers one more reason to try the Linux experiment and cut the Windows license costs. It's a pretty good reason too. Gaming was one of the very few things that couldn't be fixed easily through some other means like Wine or VMs.
If I want to switch playlists while gaming on Windows, I have to hit Ctrl-Alt-Delete, click Task Manager, then click the web browser in the task bar on the bottom. Linux Mint with Cinnamon snaps me right there with an Alt-Tab.
I want gaming on Linux if only because it would light a fire under the manufacturers to fix their god damn drivers.
I use arch on my other machines, and naturally that is a whole other story I wouldn't even dare tell a less tech-savvy person.