The point is that you have to plug it in (I don't think there's anything as nice as an actual cradle -- I think you have to actually plug a cable into the iPod) and it's either going to sit proud of the dash or in an inconvenient location. (Note that al of the places you mentioned are "outside the dash" -- I was just trying to be succinct.)

The only thing that you gain from this type of setup is not having to copy your music to multiple devices and you still have to deal with the iPod's relative lack of features.