Nick,
a more reasoned response might be: "why don't more manufacturers provide sets of graphs so that the HV curve can be derived for any given set of weight, altitude and temperature, such as that found in the Bell 212 FLM?"
The graphs most FLMs have are simply there for the regulations and not directly relatable to day to day conditions.
Interestingly, according to a conversation I once had with an ECF test pilot (now head of Flight Test), there was a move to try and miss out the testing altogether on large expensive multi engine types, as it invariably resulted in a 'crash' at some point in the proceeding with lots of bills and delays.