There are many factors including skin tone rendition, shallow DOF, and so much more, but one of the forgotten reasons is the dynamic range of the camera. Most video cameras can’t do better than 8 stops, but Art Adams just ran some tests showing the 5D achieving 10 usable stops of latitude. This is impressive since film is around 13 stops and the RED One is barely over 11 stops.
Shane Hurlbut recently talked about this when he was shooting a sunset. When a normal video camera would clip to white, the 5D produced a beautiful gradient of orange to yellow.