I certainly am not interested in any blame game here (operator's maintenance vs Boeings design) but to me the issue is how a minor malfunction (loss of the bolt for whatever reason) could lead to a catastrophe.
At the minumum the regulator needs to relook at their assumptions in the basis for cetification. And even here I'm not to prejudge the adequacy of the regulations. As I opinioned earlier the regulations are not in them selves foolproof in preventing accidents and do accept a level of risk for things that can not be contemplated.