That's like saying "software should become bug-free over time." I'm not sure it's actually getting worse over time, but it sure isn't getting better. Have you ever had to find a bug in a Wordpress plugin written in PHP by a part-time developer, that generates JavaScript, that in turn generates buggy HTML? I doubt wonky driverless cars trying to optimize a bunch of conflicting metrics (operation cost, utilization, revenue (from fares/ads/analytics), security, etc.), plugged into a constantly updating global mapping system, will have a decreasing number of bugs over time.
Google has an insane level of motivation to wring out any and all bugs from a driverless car. Even a single deadly accident in one of their cars could potentially destroy their entire business. Comparing that type of software to a Wordpress plugin makes no sense. The potential cost of a bug is huge in this case thus you will get very good software with any driverless car.
Eventually it might, but that assumes that all cars will be driverless. Even if driverless cars have a 0 error rate, human driven cars will run into them at at least the same rate as they run into static objects.
At any rate, this eventual reduction in insurance is why I started by saying "Initially at least". With time, the cost of manufacturing self driving cars will also go down.
