Looking at it from purely a safety standpoint, I wouldn't want a touch screen that spans nearly 10 inches as my main deck in a car. It's so big that you'll have to take your eyes off the road, hunt around the 9.7" screen, find what you want, and tap it with your finger.
Compare that to a "classic" deck with physical buttons. Give me a few hours with any classic deck, and I'll be able to operate it without looking at all.
I do use my iPad to play music, but I operate it with the screen off. I've configured Activator to allow the volume buttons to control next-track, previous track, and play/pause.