I havn't responded mostly because I am baffled. I have not seen the difference in control power or damping in left vs right in the first place, and intend to look some data up to see.
The tail rotor is a possible answer if the effect is real, but the typical Jet Ranger has a very low tail rotor, so there is little roll effect into it. For an S-76, the TR is large and high, but the roll effect is not apparent to me.
I would subscribe to the opposite effect for US helicopters at altitude and at mid to high speed. Left rolling maneuvers unload the retreating blade, and so are much snappier than right rolls, which demand more lift from the retreating side.