I think the point here is that most people who use the interface a few times will learn the necessary key sequences. This learning can happen with the car at rest, and after that the user can keep their eyes on the road. It's not perfect, as some people have a slower learning rate than others, but it's sure better than a touch screen.
Well, if the control all change in meaning depending on the interface state, you can only memorize sequences if there is a reset somewhere. And those will probably be very cumbersome sequences.
A "home" is a reset. A "back" button won't solve the issue.
On a second thought, if the options are hierarchical, the sequence of clicks may not be cumbersome at all. Also, in a car the state can be something really easy to keep track of, like "the car is running", but even then, I'm not sure it's safe to rely on this.
