I'm not sure about bicycles, but I've had friends die on motorcycles at under 40 mph, and had other friends walk away from 180+mph (on the track) lay downs.
Sometimes life is unpredictable. The real questions are what you hit, and how you hit it. The speed required to do damage is actually rather low, but the conditions under which those low speeds actually DO do that type of damage are amazingly rare.
-- James