Not sure about the 73 but for the 777 here goes:
The auto pilot has no input to the rudders or ailerons during normal climb/ cruise/ descent, only during the app with flaps not up (This is why the fly by wire can not compensate). So the flaperons are the only control it has available.
Kenparry is right, rotoating mass torque is very small, but the airflow has the "twist" taken out of it by the airflow stab fins, but in doing so they are subject to side forces, if viewed from the back, they are twisted clockwise.
This results in a net twisting of the whole engine assembly.
We effectively have a captured gyro, moving forward, spining right, so preccession is left, causing the right wing to rise. The auto pilot puts in flaperon to compensate. By trimming right wing down, you are taking this load to the rudder, which is lower drag for the same control result (due to moment arm ) and a more efficient flight.
In the 777, amount varies with power, speed (TAS) and engine type (Fan Diameter and mass).
Some older turbo-props had offset rudders to compensate (2 Degs for the 748/Andover) Not sure about newer ones.