The straight word I have read is that the early helicopter days after WWII were decisive.
The first helos at SUD (much later to become EC) were copies (built from parts) of the relatively successful FW 223 twin rotor.
The French started single rotor helicopter work with half that basic drive train, but chose the half that turned the "wrong" way.
Remember, the engines were developed for the aircraft in those days, and they were all pistons (and easy engouh to reverse rotation).
Here is a web site that discusses those days, but does not specify the directions of rotation:
http://www.helis.com/timeline/aerospatiale.php