On the 2G iPod, the charger connection doesn't appear to be detected. It was (still is?) a problem on the 4G (FS#5826 - no "charger status" in iPod 4g Gray) too.
I've worked out the GPIO inputs to monitor to detect external power, but I don't know what mechanism is used to pass this info to the WPS to allow the charger status to be displayed.
Can someone offer some pointers?