Like Paul and Sven have said, the outer sheath should be held by the strain relief inside the plug. I suspect the reason for the cheating is that with a grounded cord as seen in the picture, there very limited space inside the plug.
It is not an immediate hazard, but with time the small bending radius will destroy the wires, creating a fire hazard and/or shock hazard.
Just my $ 0.02 ... sorry... € 0.02
