The only take away here is that you have to treat malice and stupidity the same. The person in question either messed up intentionally, or is too stupid to do their job. You should fire them, or quit, whichever position you happen to be in.
Stupidity can also be more subtle. It's not always clear cut idiocy, there's a continuum between total and absolute head-desk stupidity, and ignorance or information blindness that's outside one's control.
Whereas malice is much less a continuum: the only question is, to what degree is this person an asshole, and when will they strike next? Intentionally and willfully hurting others is another world from anything unintentional.
The law treats it the same way. Hence, I believe it is helpful.
In any case, it's a razor: it separates illogical conceptual rabbit-holes from that which is more likely to be true.
"Never attribute to incompetence that which is adequately explained by bad management."
It's a leftover from a time when I unfairly criticised a number of programmers who were actually heroically fighting to deliver a quality product under bad management.
This is very Deming-esque, you know? http://en.wikipedia.org/wiki/W._Edwards_Deming
When a person is working under good management, with the autonomy to do what they need to be successful, the ability to get better at their work and master a field, and a clear purpose, responsibility is a given.
It is when individuals are falsely given responsibility for things they cannot possibly control that personal responsibility loses its credibility.
You don't have to blame management (or the system you're in) every time (and most people don't), but you should every time it is true, to preserve the very idea and value of responsibility itself.