I believe their thought is that the closer we get to complete automation, the less likely a driver is to remain aware. We're only at roughly 10% automation right now and drivers are already taking their eyes off the road. When we get to 90%, humans will have an even tougher time retaining attentiveness. Watch their talks to be sure.
Google's self driving car group gives some awesome transparency reports every month, including details about every accident [1]. It's like they're ready to become their own company.
Fortune had a good article critiquing Tesla's strategy vs. Google's and other car companies' [2]. The author says Tesla is being defensive and resistant to public critique. Other companies expect pushback from the public and incorporate that into their product offerings.
[1] https://www.google.com/selfdrivingcar/reports/
[2] http://fortune.com/2016/07/11/elon-musk-tesla-self-driving-c...