I think you are right about not putting your hands out for a crash, while moving. I took qymnastics one winter to learn how to fall. It helped a bit. It's best to roll up and land across your shoulder blade, upper back, if you can think about it in that instant you are flying through the air. Landing on your shoulder can mean a broken collar bone.
If you are clipped in at a stop sign and are simply falling over, then it might make sense to put your hand out to catch yourself.
I came up with an idea a while back for a set of shoulder pads for cyclists. Some sort of mini football type shoulder pads. Hopefully the pads would spread out the impact from a crash across your shoulder and thus prevent a broken collar bone. Anybody have an old set of football pads they are willing to cut up?
Or a pocket in your jersey across your shoulder that a elbow pad type of thing would fit in, to spread out the initial impact.