SASless:
Well stated. But the problem still remains.
I know of no civil flight manual that gives any benefit for headwind for takeoff performance - there may be some that allow it for Category A, but I believe you have to factor it by one-half even then.
And how do you measure the wind speed at the place you are in the helicopter? Even if ATC gives it to you, it will be measured somewhere a long way away from your current location.
Do oil rigs always have an anemometer that is telling you instantaneous wind?
More reasons why we need a good low airspeed indicating system!