Gumpy, I am glad you raised the point of the 707 and how it shows how an aircraft if supposed to act. The reference to the 707 compared to the 737 is interesting, and I believe that it brings up the point of the influence of the external environment. Why do I highlight this? Has every 737NG over run lead to a hull break up? No it hasn't. The 707 clip is in a controlled test environment, so you can eliminate potentially nasty variables out of the equation. You have to ask yourself was there anything in the environment surrounding these accidents that could explain the break up? I don't know. What was not present with over runs such as the Southwest Overrun at Midway that lead to the hull staying in tact?
One lesson in aviation is that you are playing with people's lives here. The DC10 is a great example of money v due diligence where the money won. I guess the 737 had an unidentified glitch in the rudder controls in the classics, the MD11 can be a tough one to land, and Airbus Rudders have come under the microscope after AA587.
You would hope that if this was identified as something that could lead to an inflight break up, that Boeing would ensure steps were taken to mitigate the risk, and not just sweep it under the carpet i.e MD and the DC10.
Time will tell.