A human 'gets tired', a computer dosen't. So all those cars on the road, the traffic jams, the bad driving, all adds to overall fatigue of a driver, so you may not be in 'control' as much as you'd like to think you are after a while. A computer is always ON in 100% capacity (unless its faulty, whereas you would be alerted to this so to not be able to use it)
I feel the driving test is pretty tough, but voting for re-sits is just a way to basically tax poorer people, completely unfair. Cars on the road...well yes, but thats political