Head Turner, 407 and rotorspeed,
You have all shown that you really understand the concept, and all your questions are valid. The problem is that the current regulations that we work to were made before it was realistic to be able to determine the actual usage so they froze the state of the art back in the 1950's. Changing the regs is a massive effort that requires a series of civil servants to stick their necks out and advocate change is a more liberal direction - after all, today's system works, so why risk my career messing with it? Remember, the CAA/FAA/JAA don't spend 5 cents operating anything, right, so there is no advantage to changing anything.
Look for a new presentation on my web site discussing this, maybe today!