Technically, Linux is free and so is Mac OS X. In practice you pay for them either in your own work or when you buy a machine.
Today if Microsoft charges an arm and a leg on the Windows OS, people would just switch to something cheaper. Linux and Chrome OS is good enough, and free, and even a $400 tablet is overkill for what most people do at work on their computer anyways. Microsoft will be committing suicide if it is trying to charge $100 per consumer these days when a PC is typically $300-700, rather than $2000 back in early 90s.
Steve Balmer was fired because he was milking consumers via anti-piracy rather than developing new income sources. Windows CE / Mobile failed, MS cloud is ok, XBOX is doing well, Surface is not doing as well as it could have been. Steve Balmer should have been fired 10 years ago and windows should have been free since then, but charges consumer app store and in app purchase instead (or add netflix style services to it).