I don't see how that can possibly be correct, at least for commercial airliners.
An airliner will use maximum power at takeoff, somewhat less for climbing, and much less during cruise. The figure I see is takeoff fuel consumption/hour is like 3x cruise fuel consumption/hour. Power needed will also decline as fuel is burned off, since the required lift goes down.
Thinner air. Engine is not capable of burning as much fuel, or generating as much thrust, with full performance at cruising altitude.
Ah, that explains it. Thank you.
Couldn't this just be related to relative engine efficiency? You could easily be running the engines effectively full power the entire time, but obviously high-altitude cruise is where you spend most of your time and presumably the engine's are optimized for that operating regime.