If Obama is not on the ticket (and how could he be after Hategate?) then black will stay home or (gasp) vote for McCain. Problem solved.
Yep the black vote is important in a number of states.
The Dems. will have a hard time in PA without a strong turnout in Philadelphia. Ditto in Ohio with the need for a strong black/Dem. turnout in Cleveland. And Michigan Democrats depend on a strong turnout in Detroit to offset the rest of the state. If lots of voters who have been excited by Obama stay home rather than vote for Hillary, then McCain gets a big boost.