In reply to:

I get slightly peeved when someone misnames me, but actually I am interested in why this should happen so often over a long period, as far as I remember only with Americans, and always to Ron, not Roy or Rob, Tod, Red, or any other appellation.

I speculate that it is because "Ron" is a common name in the US, while all the others - Rod, Roy, Rob, Tod and Red - are relatively unusual. I have known many Rons in my life, but only one Rod and two Robs, and no Roys, Tod(d)s or Reds.