Steve,
I think you are over simplifying things with your assertion: the HV curve applies at any pertinent stage of flight be it take off, cruise (power line inspection?) or landing. What changes is the size of the curve and its effect.
You must remember that the curve is based on level flight at maximum weight. If the a/c is descending then the power demand for any given speed will be lower and the effect of power loss reduced, hence conversion to an OEI descent and landing easier. If the a/c is climbing at the same TAS then the power will be higher and there will be a period during the entry to descent where the Nr will tend to decay more rapidly, hence making the phase more critical. level flight will be somewhere in the middle. The higher the speed the less variation. The greater the rate of descent the smaller the curve will be.
There will be some weight and ambient conditions where the HV curve is non existent: how else would you be able to certify a Cat A helipad profile and hence the often prohibitively low RTOWs associated with them.
How do you think the LDP is choosen on landing? One consideration is the balked landing case and the obstacle separation requirements associated with that, but the other is the OEI landing case.
I hope that gives the general idea; the HV curve is not a fixed entity and represents the worst case scenario. It may or may not be present depending on the weight, ambient conditions and whether the a/c is climbing, level or descending.