I wonder what happens if the radio DJ says something like "set the aircon to 20 degrees" and the voice command system hears it.
And what happens when your kids in the back keep shouting out "turn up the volume". Or when they argue about whose music to listen to: "Play CD 1", "Play CD 2", "Play CD 1", "Play CD 2". It would drive you nuts.
The company I work for makes automated phone systems. The type of systems where you call up, select from menus, say or dial your account number etc and if you are really lucky you will eventually get placed in a queue to speak to someone in an indian call centre.
Businesses LOVE these systems because they can save money on staff to answer the phone. And the longer they mess you about, the more money they make on the premium rate phone call.
Customers HATE these systems because people generally don't like talking to computers. When somebody calls up, they want to speak to somebody with a brain who will understand their problem and be able to help. But instead they get "say sales or complaints", "compaints", "did you say sales?", "no", "say sales or complaints", "compaints", "I don't understand, please try again"......
I think it would be the same with voice commands in a car. I don't think customers really want to talk to their car. At least not until it can understand and talk back on an equally articulate level. Speech rec technology was pretty poor in the 1980's. It has advanced a long way in the last 20 years but it's still crap.