as alluded to over on AppleInsider, Google seem to want to put Android in the car, i.e.: the car has it own OS, where Apple want it car to pair with your phone and use that as the 'brains'.
Seeing as cars have a much longer life span than a phone, Apple route seems to be the best, as you can upgrade your phone as much as you want and the BT/Wifi/Dock link will still work and use the newer and faster 'brain'. And all your content goes with you to your new car, in case your car is stolen or you total it.
With Google/Audi, your car hardware will be very obsolete within a short time.
The Google/Audi approach also lends itself more to the scenario of having another monthly bill for your car.
I, for one, would definitely walk out of the garage if the salesman told me this new car has Android on board.
Then again, I am one of those people who would never buy a new car again. Once bitten etc. (unless I win the Euromilions!! )