Well, boys, I had a chance to talk to the tech guys at Robinson. Its the engine, not the MRG.
Proof: The gearbox in the Raven II is exactly the same as in the Raven I.
And that is why I believe it IS important to understand HOW the limits came to be as well as WHAT they are. If I'm in a crap situation, which I intend never to be as I do this just for fun (in fact I have a rule: at the first close call of any kind my Heli flying is done), I know I can pull takeoff power as long as I need it, and the result will be wearing the engine out sooner, NOT falling out of the sky due to a catastrophic failure of the gearbox.
If you want to go down the "just follow the rules" path, why bother to teach aerodynamics at all to student pilots? Just tell them "As you are slowing down, once it starts to shake around 20 kts you will need more power until you are really close to the ground"