I would also suggest that during the design and certification of the system, the safety analysis assumed a trained and competent aircrew, too. With hardly any change in such assumptions from the 60's and 70's.
With the exception of the 787, the autothrottle cert basis on all Boeing aircraft was for a 'Design Assurance Level' (DAL) B or C system (depending on which aircraft) - 'flight critical' is DAL A. In other words, a DAL B/C system doesn't have to be perfect, because it's assumed a competent flight crew will notice if the A/T isn't doing what it should and intervene... It was something of a hassle for those of us on the Propulsion side, since we had to assume the A/T could do something stupid so we needed to design our systems to account for that. I don't know if that little tidbit - that the A/T is
not designed or certified as a flight critical system on most Boeing aircraft - is included in the flight crew training, but if it's not, it should be...
My understanding is they finally upgraded the DAL of the autothrottle to 'A' on the 787 (although I don't know that for a fact).
And at the end of a 14 hours sector after some dodgy crew rest, making an approach in tricky conditions at an unfamiliar airport in a new aircraft in your window of circadian low, I can see how all the factors stack up to make an accident like this more likely.
I don't dispute that fatigue likely played a factor in Asiana, but what part of landing at SFO on a beautiful, clear, sunny summer day would constitute 'tricky conditions'? If a pilot can't handle a near perfect summer day without hitting the sea wall, what chance would they have at night in a storm?