Microsoft is preparing its community for the arrival of Windows 9, probably sometime in 2015, but that will probably be the last operating system that Microsoft will sell. The Linux systems are evolving quickly and the there's no stopping them.
If you remember correctly, Apple already took this step, of making their system free (sort of). A mix of factors, like the global economic crisis, the launch of Steam for Linux, and the increasing number of developers who are willing to make their application available on the Linux platform, has turned the open source world into a freight train.
Maybe not everyone has noticed, but the Linux platform has evolved in the last couple of years more than it has done so in the last decade. NVIDIA, AMD, and Intel are actually starting to provide proper support and the driver performance is catching up with the Windows platforrm.
In a couple of years, most of the games released on Steam will also be available on the Linux platform, and so will happen with most of the applications. It will become increasingly difficult for Microsoft to justify asking a price for an operating system that has an equal counterpart that is already free.
Making Windows free will force Microsoft to look for other ways of making money, maybe from support for corporate solutions, for example, or from selling other proprietary software.
In any case, if you are a Windows user, you might want to start learning some Linux skills, you might need them in a few years.