Ipods used to support firewire and USB charging, which both used different pins on the apple connector. At some point apple decided to drop firewire charging to simplify hardware and software and there fore left a number of after market accessories unable to charge newer ipods the switch was about the time that the ipod touch and newer metal nanos came out.
In VW equipment terms that means that the older style ipod adapter that behaves like a cd changer wont charge the newer ipods, not heard of these adapters that allow charging but would be interested in a link. As old Bose equipment used firewire so I'm currently stuck with my old ipod video in the sound dock portable