Believe me, it does touch the anodized metal plate as there is no insulating material between the circuit board and the plate.
As to shaking and or banging the unit, you don't need to do this for there to be problems.
From the point of manufacture, to the shipper, to the store, to the time you get the router setup, there is plenty of opportunity for the router to be shook up and or banged enough to scratch the metal plate to cause any possible shorts.
Like I said, all units may not be affected by this, but it is a flaw in the manufacture of the unit.