I'm not. With software so ubiquitous and even required to use a computer, why shouldn't the cost of entry be as low as possible? Your browser is free, your media player is free, Steam is free, why isn't your operating system?
Because microsoft has a sizeable grasp of the OS market, a very recognizable brand, and people are willing to pay money so MS charges. However, that says nothing about the quality of the product. I love my $100 copy of windows 7 64bit, guaranteed compatibility with any programs I could ever want, ease of use, driver support, etc. I installed a ubuntu partition on my drive to get the linux promo for TF2, it was extremely slow and laggy. I had to install 50+ packages for steam compatibility alone.
ON THE SUBJECT OF WINDOWS8/8.1:
It's a trainwreck, of microsoft's own design. I don't think it's indicative of windows in general. I don't know why MS would make a new OS that takes away some major UI that most people like for a tile interface and breaks a little compatibility, then release a service pack that adds the same UI back from 7 that also breaks more compatibility