Car Manufacturers are using the iPod dock interface because it's what the masses have (the iPod). It's the same reason why you see so much stuff that supports iPod docking. Because since Apple's marketing appeals to so much people that alot of the masses have some iPod device (and I think all of them except the iPhone 3G) all share the same connector dock.

I just avoid it all and buy stuff that isn't limited to just the iPod. (for example if a stereo has a line in option). Which is why when I'm buying a car, it won't matter if it has an iPod interface (heck I might negotiate not to have it included to lower the price). What I want is an input for audio. (right now I'm using this old tape plugin since my 94 camry does not have a modern stereo).

Edit: I find the speaker interesting though. I wonder how loud it is in comparasion to the IPhone's speaker. (cause I've compared that to the n800's speaker).