I don't have anything to add to many of the comments already posted but I'm reminded of Cyanide and Happiness very poignantly making a similar point: https://www.youtube.com/watch?v=fAKQ7ouQqgA.
The choice is about releasing version 1.0 vs constantly adding features that are better suited for versions 2, 3, 4+. What can be done now, at reasonable cost and technology level? My position is that we could have a system right now that would alleviate traffic congestion and offer greater safety. Advancement on the harder problems comes with real-world experience in the field.
I don't think any of those examples are edge cases. The first set are normal traffic conditions that in the context of self-driving cars are easy to solve, especially in narrowed conditions such as on a highway. Moreover, mid-range cars already have collision warning and automatic braking systems. As to your example of traction issues, pretty much every modern car that I'm aware of has had computer assisted traction control systems for a while now.
The edge cases that are difficult essentially boil down to entity recognition; unexpected and moving obstacles, road sign changes, traffic light outages or alternate signal pathways and the like. Some of those definitely would require government level coordination which is about a lot more than technology.
I think a more fundamental problem here is that self-driving cars are as much an infrastructure problem as they are a technological one.
As an analogy, consider hybrid vs electric vehicles. In places like North America with large, open spaces, electric vehicles really only serve a specific type of urban driver. The culture, infrastructure and geography dictate 600km distances which really aren't practical at the moment with current battery tech. Whereas hybrid vehicles can (or could) quite easily reach that range with options to recharge once you get to your destination or have a longer stopover and still use existing infrastructure. The focus on purely electric is a lost opportunity for anyone who needs power or long distance.
Similarly, cars could be designed to be self-driving in the easy cases; highways, certain urban thoroughfares, particular times of day and the like where existing vehicle and pedestrian flow patterns eliminate the edge cases. coordinating systems along the aforementioned types of roads could be installed as was done for cellular service and GPS and other protocols could be developed to ensure safety and reliability as well as fallback in case of emergencies.
Instead, we've decided on all-or-nothing bets which don't move things forward--or at all--and my worry now is that we'll lose an opportunity to pick the low-hanging fruit and solve the harder problems incrementally over time.