Air bender,
Good point, and worthy of comment. The weight is not as great a factor at the bottom end of an EOL as you might think (USL notwithstanding - that's different!).
I have flown/taught/sat thru over 800 engine-off landings (yes, really). As long as they are handled properly, and the Nr is conserved throughout the descent and built during the flare, the weight is a relatively minor factor (although still a factor).
This thread however, is a theoretical debate. Most pilots (not all I admit) are not thick, and will hopefully see the difference. I am not, for one second, advocating being light or heavy in auto, and unless you have a load you can pickle it is a moot point anyway - not gonna throw out a passenger when the gearbox lets go...although I did carry Michael Portillo once...
I simply want to know why a heavy heli descends slower than a light one, all else being equal. It does, and it seems wrong. Contributions here (and some people have clearly expended some brainpower) show that others are not sure either.
That said, I take your point, but believe it to be somewhat misleading in that when you have an emergency requiring autorotation, you weigh what you weigh. You enter auto, recover the Nr, turn into wind if you can and select a landing point, diagnose and deal with the emergency, put out a mayday call, secure the engine if there is time, and whilst doing this you manoeuvre the acft to make your chosen landing site. You fly the acft you have, and use the performance it gives you to achieve what you can.
But I still want to know the answer to my question - things are becoming clearer from the replies so far.