"Nearly replace" it's always that last 5% that takes the vast majority of the time.
If it was really as great an idea as you were saying we'd already be doing it.
I'm sure it'll be got to work on the motorway, where the roads are well defined, and even the expense of ultra-detailed mapping won't be a big issue. Additionally you aren't going to need large numbers of software updates because the roads themselves rarely change, and when they do you get lots of notice. You also don't have pedestrians, cyclists, horses etc to worry about. You also never really have to worry about skidding as long as you stay within the speed limits which are far lower than the effective design speed of the road.
I'm sure also we will have automatic braking which will be useful everywhere and advanced stability controls. And perhaps we will have a dummy mode where the car drives itself slowly home from the pub when the driver is drunk. And all of that together will reduce accidents by 80-90%. It isn't going to save me driving my morning commute though.
So basically two of the most important countries.