Oh my goodness....
having recently qualified as a domestic electrician where the emphasis is on ensuring you have earth paths down to the mass of earth
You do understand why this is so?
The Earth connection used for buildings is nothing to do with the flow of power (current). The Earth connection is for SAFETY from lightning...
A building Earth rod is used to ensure that a lightning strike on a house that finds its way into the electrical wiring has a path to ground.
It is most CERTAINLY not to prevent shocks due to equipment faults, etc. Shocks are prevented by tying the earth wires to the neutral back in the fuse box. The earth wire acts as the last line of defense should you decide to drop your toaster in the sink - since the manufacturer will have connected the nice metal case to the earth pin of the plug - this forces the current flowing down the "hot" wire to flow back down the safety earth, and blows the fuse. Normally the working current returns down the neutral, but the fault current flow will be many times the working current.
In a vehicle - car, airplane, etc - there is no path for lightning to ground, hence they are not EARTHED. The internal electrical systems have a "return" or mis-named "ground" but this is to provide a return path for current to flow (and hence do work). Current MUST flow in a circle... from source back to the source (hence the name "circuit").
(Even so lightning can obviously still hit an aircraft and cause nasty things to happen, but nowhere near as bad as if the aircraft were joined to ground).
- GY