I play right handed with a mouse, and I can't imagine spinning counter clockwise. It would feel really weird. I think I tried it once or twice, and I couldn't control it well, so I never tried again. When I started playing I just naturally spun clockwise, and I've been doing it ever since. I think I'm not the fastest spinner out there, though. I probably average 300-350 depending on how serious I am taking it. I can spin faster if I really try, but probably not sustainably for those long spinners.
My theory is that it's possible that different brain strengths might affect what direction you naturally want to move in, or possibly past muscle memory learning from other activities. However, I do think that naturally the fingers will want to draw circles in a counter clockwise direction when using a pen, because your hand has more strength in that direction, so I suspect few tablet players spin clockwise when right handed. I assumed, at first, that all mouse players would spin clockwise, because most of us are used to having a keyboard directly to the left of our mice, and naturally your body would want to move the mouse away from that obstruction. Also, the motion is similar to pealing with a knife, or other similar activities. Those are my thoughts on it.