Microsoft xbox operating system provides xbox programmers with a set of common standards to use to access controllers, the kinect motion sensor, play sounds, draw graphics, save files, and more. without this, games would:
a) be more reliable.
b) be a lot easier to write.
c) cost more.
d) look same.
e) not be restricted to just microsoft's platforms.

e) not be restricted to just Microsoft's platforms.

Explanation:

Microsoft provides the Xbox programmers the with common standards to use that are already set to access controllers which includes kinect motion sensor,save files,play sounds etc.

Kinect sensor consists of following components:

Without this the games would be run on any platform not just on microsoft platforms like sony's playstation etc.