Comfortable, or tolerant?
Here's the thing: those faithful love Microsoft. There's a reason that most (90 per cent!) people happily prefer Windows to Mac OS X, and buy Windows machines. They're comfortable with the experience.
Shall we say just that they are more comfortable with that experience than they would be with the cost of buying a mac or with the bother of removing Windows from the PC and installing something else?
That's what it comes down to, for most people. Windows is what came on the PC when it was bought. It's hard to buy a PC (apart from a Mac) that doesn't come with Windows.
There are a few alternatives -- you can buy a laptop from HP or Dell with Ubuntu preinstalled -- but the choices of hardware are limited and neither it nor Ubuntu will run CallOfGrandFifaFlightShooter, which is all they really care about.