I should start out saying I agree with all the comments above, namely people who get into danger with a satnav are just bad drivers, full stop.
I can understand the slight difference though, in that humans are generally inclined to "trust" a "human" who has earned it. In this case, the satnav is (to all intents) a human voice and has earned trust through hours of being correct, the natural human instinct is to trust the satnav's voice.
Although having said all that, even if someone was navigating with a map next to me and told me to turn left, I'd still notice if it was a no entry sign for example and explain I can't do that. I'd also be able to figure out if a road I was about to enter was too narrow for the vehicle I was driving, recognise a grass field followed by a cliff and notice a user-operated level crossing when I saw one.
I also don't see how updating map-makers data will get to my mother's satnav without me intervening, taking it out the car, plugging it into a PC, updating the maps, hopefully not buggering it up... Satnavs live in the car, and without OTA updates will seldom be updated.