If this is valid - arguably a big "if" - it seems to me to be not unlikely that the keyboard would be used to provide input to some iPod function, not just serve as a dock. Just an idea. iPhone dock, anyone?
That or for 5th generation iPods to serve as some kind of secondary screen, and or to be used as a dock to watch videos while using the speakers of the computer that it is connected to (or any speakers or sound system connected to said computer). I would actually use the 2nd feature allot. I tend to watch videos on my iPod while I do other things (processor intensive) on my computers.
Every CPU cycle counts when you are working on video editing