I recently purchased a 30GB "iPod with Video" and it included the dock adapter, so the previous review is actually misleading. Note, however, that the Universal Dock (which I also purchased) does NOT include an adapter for the "iPod with Video."
So, you only need to purchase this adapter if you (a) lost the adapter that came with your iPod with Video, or (b) want to use TWO Universal Docks e.g. one attached to your computer and one attached to your stereo/television.
All of that said, I agree with other reviewers that Apple is nickel-and-diming its customers by selling so many seemingly optional doodads separately. $8 seems a bit steep for three little pieces of plastic -- two of which will never be used.