I must say that's interesting. I'd like to see stats on the Kenwood deck though if you can kick me a URL. I'd love to get a view of how it works.
Now then, on the other, I'm not sure what it's excuse is. Really I'd hit google.com with "GM Hughes DataVision" and see if by chance you can find some company specs/info before even thinking about it. In car HUD systems I will say this. The display is on the windshield. Yes, I know you knew this, but that's one expencive as heck windshield. Automotive HUD displays that display on the windshield need a special layer embeded within it (the windshield that is) else you will not be able to see anything what so ever.
Thus why I'd like to see the Kenwood one. Unless they provide a clear stick on sheet of plastic, I'm not sure how it would display. Be very nice to know.