It's a hint, like lane lines. You're going to be using GPS and LIDAR as well. Yes, some of the lamer self-driving systems put too much faith in lane lines.
Indeed. Which means that we're back to square one, "it's where most people are, which is exactly the spot where it's least needed; whereas in places where more conventional navigation fails, there's minimal incentive to also build and maintain this."
TL;DR: good roads will be getting better, bad roads won't.
TL;DR: good roads will be getting better, bad roads won't.