Edwards and Kerry are being used in EXACTLY the same way: Send them out, and let them give some face-to-face love to the base. Small speeches, small crowds, red meat content, no big TV splashes to take attention from the main guy.
Both campaigns have settled into what now appears to be their true strategy: nurture the base. For months, Kerryistas went after undecided voters, but there weren't any (there are undecided people, but they decided not to vote!). Now, Kerry is going to try to turn out the faithful. This has been the strategy of Repubs/Rove since May or so.
Neither Edwards nor Cheney are effective headliner campaigners. (Edwards could be, perhaps, but he is no longer trying, and has accepted his good soldier role). Both are good at delivering ideological wet kisses to the hardcore supporters, though. People have been saying that Edwards, in particular, has disappeared. But that's not true. If Kerry can get 75% of the people who honestly prefer Kerry to Bush to vote, he can win easily.