I would be curious as to what pedals the fallers vs the non-fallers are using as well.
I have fallen 3 times during the first 4 years of cycling. Those were on the Look Delta system. I never fell on my Speedplays or SPD-SL's, nor on SPD's or Onzas on my mtb, but it might have something to do with my experience by then since I haven't fallen since my 4th year, which would be 12 years ago.