I've been riding nearly 50 years (started when I was 4) and I can only think of 2-3 times when a horse deliberately bucked me off. Stopping in front of fences, now, that's a different story - that happens to me ALL the time although less since I switched from hunter-jumper to combined training, since I'm sitting deeper in the saddle and thus less likely to get "launched".
And you know, I'm willing to bet that the few times the horse took it into his head to ditch me, it probably WAS my fault, and I just didn't realize it at the time.
My last fall I knew was coming before I even left the saddle. Sam the Perch was cantering around the ring, and I was doing that fluid thing with the torso and arms to keep in the rhythm, and I lost said rhythm and knew a trip to the ground was in my immediate future.
My buddy Angela said it was one of the most graceful falls ever. She taught me most of what I know about how to fall, so I trust her judgement. ;)