I think I know the answer.

In one race DH and I did on the tandem we started at the front of the entrants.

As we are not fast cyclists this meant we got passed by the elite riders etc in waves.

The faster rider bunches did have crashes but they were amazing to watch. I think it was a combination of speed and skill that the riders that crashed seemed to "tuck and roll", quickly got up and again and got on their bikes and raced off. WOW!

It wasn't until later with the slower people with less skill that we saw BAD crashes. Like lots of blood, wrapped around a power pole and out cold crashes. The faster, experienced bunches actually rode safer and called hazards (or pointed) and had faster reflexes. The slower people did more silly accident stuff like touch wheels.

I also was in one race (on the tandem) when one guy's front tyre blew on a downhill. Becuase he was in a bunch of experienced riders, the guys next to him grabbed an arm each and actually used their brakes to slow him down and then move him off the side of the road. Otherwise he would of taken out the whole bunch.

I think experience is one factor in avoiding broken bones (says the person who has broken a collarbone due to a stupid rider in front of her and a shoulder- this time due to her own inexperience.)