The examples given seem more like inattentiveness than stupidity. Which makes sense. Attention to every detail requires effort (a lot of effort). Sometimes one person may not have all of the resources required to pay enough attention to every detail. The ones you pay attention to (e.g. aircraft maintenance) account for fewer problems.
Throughout my programming career, I've noticed a strong correlation of bugs with code that was given less attention (it was deemed to be an easier problem to solve, or compartmentalized and solved later).
I don't think it's fair to claim people were stupid just because a detail was overlooked. Perhaps they could have allocated their attention differently, but without knowing all of the trade offs it's hard to say they made a bad choice.
I think that people have a finite amount of "attention" that they can devote to things during a day. Furthermore spending attention on a task seems to consume energy. It's reasonable to think that occasionally some items get less attention than they should.
