Car-to-car communications are not necessary for automatic driving. They may even be undesirable, as a potential source of bad info. Google/Waymo doesn't need them. They make the point that there are lots of things in the environment, from bicyclists to moose, that aren't going to cooperate with the system.

The need for super-detailed maps is probably temporary. A reasonable goal is to have the ability to drive anything with a basic map (Google StreetView level) at slow speed, then retain info to do it again at faster speed. Some of that mapping info may later be uploaded for use by others.