Reading this thread drove home for me the point that diving disasters are in a way more "decisive." If anything happens beneath the surface and you don't get rescued within the hour (usually less), you are probably dead from the lack of air. No herculean tales of human endurance there. If something happens on the surface (e.g., the boat loses you), ah, I suppose there are more possibilities, but you aren't exactly going to start a fire to keep warm.