Nobody suggested a RF ground, rather a lightning rod ground. The problem is with possible lightning strikes to the antenna. Without a separate ground, the lightning strike jumps over to the next power cable, possibly destroys electrical devices or hurts persons, maybe also set fire to your house.
A discharge tube can only "consume charges" when it's connected to a good ground, it may also clamp indirect lightning overvoltage if the antenna stays connected to the receiver.
For indirect lightning effects, e.g. occuring when a lightning strike happens in the vicinity, the classical suggestion of disconnecting the antenna cable (and the receiver power) still makes sense.