I have one word to say on this topic, "OVER-STRESS". I can almost guarantee that the maneuver that broke both these airplanes, and a lot of others, was not the one that did the damage. Stress is a very insidious force, go talk to an full scale aerobatic pilot. I would love to see some one put a G meter in to one of these airplanes, I think the results would be more than a little interesting. By the way, a blender if done properly puts very little stress on an airframe, snaps at full power and high speed, well that is another matter!