James Taranto notes that Kerry's support is slipping in the black community, and uses this to explain Kerry's recent mention of Mary Cheney:
Note that the explanation for the shift centers on older black voters and Christian conservatives. Is anyone still obtuse enough to believe it's mere coincidence that Kedwards have been shouting from the rooftops that Dick Cheney has a homosexual in the family?
That said, my take is that people are thinking too hard, and overlooking the obvious reason that the two Johns keep mentioning Mary - when they think of hot "girl on girl" action, they think of Republicans. And why not? Tall John has probably been hearing from Teresa for years what we just learned this week - Republicans have better sex.