Why would they do that when you can just take your existing iPod and connect it to your car stereo. I think the right thing to do would be to get more of the car manufacturers to include ipod support by default in their cars.
I know a lot of new cars now a days have the auxilary port in there but that's not as good as genuine iPod support. And if you can find a new car that has real iPod support it only comes on the top of the line trim level of the car.