marcuste747, great question.
The problem lies in the fact that many pilots do not differentiate between THRUST, which is a FORCE, and POWER, which is RATE of doing WORK (and Work is the amount of energy transferred by a Force -- sometimes Work is defined as the product of force and distance).
Pilots often use the terms thrust and power interchangeably, but in aerodynamics we are in the world of physics and mechanical descriptions.
Muffinman relates the Vy answer back to thrust curves and power curves -- which is the correct thing to do. The reader has to remember that thrust curves are not power curves!
Broadly speaking, a turbojet engine is a thrust producing device, with output given as lb or kN. Propellors, whether gas turbine or piston, are power producing devices, output given as hp etc.
Aerodynamics for Naval Aviators has a more thorough explanation.