I sure as hell hope they're engineered that way, anything else would be hugely dangerous.
These types of systems just fill me with paranoia considering all the time I've spent wrestling with broken computers. Mechanical links fail as well of course, but they can usually be made to fail safe. I'm not sure that's quite as easy to guarantee once a computer is involved, though that may be my ignorance showing.
If I'm going to be smeared across the mountain-side I want it to be because of something physical and real like a stuck throttle wire, not programming error.