The parent was specifically talking about making hardware available for use. That's kernel stuff, not GNU userland.
But if you want to talk about userland, then you need to buy supported equipment. OSX doesn't work with a ton of equipment out there - as that equipment does not come with OSX drivers. Windows also works like shit when it doesn't have the drivers - anyone who has had to install XP regularly will quite happily attest to just how terrible it is at supporting network cards before you install drivers.
Then, of course, there's the bonus of the AMD Catalyst driver installer program for windows: at least as recently as win7, if you didn't have drivers for video, it fell back to VGA graphics. The Catalyst driver installer was too large to be seen on VGA - you couldn't see the bottom of the installer window to see what was going on, and couldn't drag the window high enough without a hard-to-discover key chord. :)
The argument to "buy stuff your operating system supports" sounds like a cop-out, but it really isn't. OSX, for example, is difficult to make run on things other than Apple-designed computers, but if you complained about it, people would write you off as an idiot.