Actually, this fits the Kerry pattern of being all things to all people. Surely, the bigots need a reason to vote for Kerry. His people know they've got most of the bigot vote, but not all. So this was his chance to really go after them.
sKerry figures that by his mentioning Cheney's daughter (instead of say, Gephardt's daughter)that some evangelical christians will not be able...in good conscience, pull the GOP lever.