Battery save function. If it's like the 5d, when it shuts down to save power, double check your WB, exposure, ISO, etc when you power back up--the 5d resets, and AFAIK, there's no "scene file" type presets.
The camera doesn't actually turn off. It merely deactivates live view. The camera is designed to do this because, on a still photo DSLR camera, live view isn't intended to be used all of the time. Still photographers, by and large, prefer to use the optical viewfinder in most situations. When live view is deactivated, you can still take still photos perfectly fine.
By default, the camera deactivates live view after one minute, if you are not recording video. There is a menu option that allows you to change the time or disable it completely.
It didn't just deactivate the live view... it shuts off the power too... as you don't see any settings on the little lcd screen on top... I think it's more of a "hibernate" mode... and you can press any button to wake it up!