Re: "so far caused by human error and inattention"
How do you know they are doing so well?
Yes they have managed OK on a pretty regular US system, but how much do they depend upon GPS/maps being completely correct? how do they cope with partially closed roads? What about twisting country roads with passing places? Temporary traffic lights? Polices flagging them down due to an accident or similar? Dumb meat-bags doing stuff that another meat-bag would see the warning signals of high stupidity and/or intoxication and keep well away?
Though Google are pop-pooing it, the accident rate seems to be about 5 times more than average, so its hardly a stunning display of everything being just right.
And Google have a vested interest in playing up the success and not talking about any known problems, do you really want to end up buying the high-tech Ford Pinto?
THAT is why there needs to be an independent analysis of what has actually been tested, and when failures have occurred, what should have been learned.