A few thoughts:
At zero airspeed, how much induced drag does the aeroplane see? How much profile drag?
How much horsepower does it then take to (ahem) "move" it at zero airspeed?
There may be a clue here...
Sure, no power is required if the aircraft is at standstill but that does not mean no power is available. OTOH power is required to accelerate the mass of the vehicle from standstill with or without aerodynamic drag. No power available = no acceleration. THP is the power available. If the aircraft has to move before you get THP then you are in a chicken and egg situation - you can't accelerate the aircraft without power but you can't have power until you move the aircraft.
The question is: if the engine is producing 200 BHP and the prop is providing thrust can we say that the prop is providing THP, even whilst the aircraft is stationary?
THP = BHP x PE
If there is thrust PE is not zero. If PE is not zero THP cannot be zero. THP is not the same as power required, though it may have the same value.
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RRT,
As an aside, the power required curve in the link you provided should be very familiar to helicopter pilots: the high power required to hover and the ‘hump’ near zero IAS as one transitions to forward flight are important characteristics for rotorheads to consider.