Kiwi,
I am fully with you that RCDs are in no way a protection against electric shock, that's what the protective Earth conductor is for.
I believe RCDs are mis-sold. I personally view an RCD as a means to detect latent faults i.e. where a current carrying conductor is attempting to return to its birth place (i.e. Earth/Ground). Usually this involves a high-ish resistance (such as water) and if it was not for the RCD the fault could escalate to a point where it becomes threatening (such as fire).
In short; The RCD is simply another component within the distribution system to protect the electrical installation and devices connected to it, and not as a means to prevent electric shock.
M.
