rigpiggy:
My understanding re RHS helicopters is that Igor Sikorky adapted the vs 300 into a two seater he placed the collective in the center. When he trained the new pilots since he was comfortable in the LHS the new trainees were RHS, then it became tradition. However when doing long lining it is normally flown from the LHS since it is easier to lean over the collective while watching the load.
I was once told it was because some early helicopter's exhuast fire created some reflective issue for the guy in the left seat. I always relegated that one to a sea tale.