The advantage of supplying 240V to a big appliance under the American system is that no part of the wiring exceeds 120V to ground. The only way to get shocked at the full voltage is to touch both hots simultaneously.
Looking at a 220-240V British/European equivalent, there's only one side of the circuit which will deliver a shock if touched, but it is at the full voltage. Everything else being equal, the current through the body will therefore be much higher.
If the loop resistance to ground through the body were a little over 4000 ohms, then touching one side of the American supply would result in a current of just under 30mA, so one could be left holding onto it without the breaker tripping. At the same resistance on a 220V line the current would be over 55mA so the RCD should trip immediately -- Higher shock current, but only for a brief fraction of a second.
Is this what you were thinking?
