Nothing,

I think that Windows' supremacy on the desktop is due to Microsoft's anti-competitive practices and agreements with the hardware vendors. It doesn't make it right.

I prefer to see a multi-cultural IT: Linux (Ubuntu, Redhat, Fedora, Slackware, Debian, ...), Windows, MacOS, Solaris, FreeBSD, .... and many others.

I don't believe in one OS to rule them all.