Keep in mind that most people who play games (and I'm not talking about Angry Birds or Facebook games but people who use Steam) tend to build their own PCs.
And installing Linux is just as easy as installing Windows, if not easier (you won't have to go on a driver hunt most of the time for instance).
Do you have a source for this?
In my view you're either a layperson who plays Candy Crush or iOS games or you know about Steam and GOG and the sky is the limit.
A standard Kubuntu (or Chakra) install on any Intel/AMD PC made before June will likely work without hiccups or missing hardware. Most distributions include an app to specifically detect/install proprietary drivers (Ubuntu uses Jockey). A browsing of Phoronix.com will provide you with benchmarks showing the NVIDIA/AMD/Intel drivers running neck-and-neck with Windows. But hey, let's not let the truth get in the way of your FUD.
I love Linux, but "if a program works on every single other distro.." is disingenuous. I have not once had 100% success with Linux on initial install. There has always been something that needed to be tweaked (usually sound or graphics). No, Windows isn't 100% either, but it's more like 98% while Linux is like 92%. For the majority of people, that 6% difference matters.
Gaming on Linux still needs to catch up. NVidia Optimus support is still being worked on. Most platforms don't ship with the proprietary drivers, which are the ones that are actually good for gaming. And from what I hear, the OSS AMD drivers are good at power management while they suck at gaming and flipped for the proprietary ones. AMD also has a problem where they drop support for cards relatively quickly.
I love Linux so much (Crunchbang, baby) but it's so fragmented that unless things change, gaming on Windows is going to stay easier. I don't see any reason why my family would give up Windows with its large library of games and all that support for Linux with its tiny library and not up to par drivers. That might not work on that distro without some workaround.