I going to take an educated guess, I think that the driver isn't telling the whole truth here. How do you let the car drive off the roadway without intervening? In all likelyhood the reason is, that the driver was not paying attention! Pilots of Airliners who fall asleep or are inattentive to the autopilot are still at fault if the automation does something unexpected and they (the pilots) fail to intervene. This is less about the limitations of the "Autopilot" but, more about about the human factors that lead to these sort of accidents.