The primary purpose of SteamOS is to make sure Valve still has a future in the event that Microsoft actually ends up walling up future versions of Windows. Supposedly, there are four types of PC user... The first, the casual user, has already drifted towards smartphones and tablets. The other three are still currently served best by Windows, but one, the PC Gaming enthusiast, will likely drift to wherever they can best continue to play and support their massive PC gaming library which is likely to be on Steam. Should Microsoft kill the desktop, and thus support for the PC gamer's gaming library, PC gamers, at least, now have an alternative backed by the biggest seller of PC games... Valve.