i think you misunderstand his appeal. as a black man he knows that will generate an active voting response from the African-American community. like the democratic party he correctly recognizes that voting block has no where else to go and with him on the ballot, instead of sitting home (like they did with al gore in '00), they will show up at the polls.
he is not asking them to vote for him because he is black. he knows that as a given. the democratic party, since bill clinton, keeps offering up party insiders who have no significant appeal to the typical unaffiliated citizen ... that is the swing vote which determines elections. while hillary touts her superior experience Obama appears to be highlighting what he will bring to the election - a certain black voting block.
hillary has a similar opportunity to appeal to women voters ... would most women not want to help elect the first female president? but it will likely have to be a woman without all of hillary's negatives. bill has all of the charisma which is resident in that family. fortunately for Obama, he has it, too

__________________
“Mayor Palin fails to have a firm grasp of something very simple: the truth.”

[Frontiersman editorial, 2/7/97]