The API comes standard for all Windows 8 and RT users, but those still smitten with Windows 7 will not be able to enjoy any of the new DirectX enhancements. Microsoft’s Dev Center details the new features which offer Windows 8 developers the ability to design programs to be fully immersed in the Live Tile experience.
The reason for the change is Microsoft’s visually intensive focus with the new Windows 8 OS. Its design inherently requires stronger multimedia support. This means that game developers will have to design new content with DirectX 11.1 as their foundation in the near future. So if you want to enjoy the latest FPS multiplayer sometime down the line, you better get use to the idea of the Metro/Modern UI.