At this point in time, ther are no “undicides”. Every individual that intends to vote have made up their mind that they are going to vote either for or against obama. Since either obama or Romney will be in the White House come January 2013, any vote not for Romney is [ no matter what the vote caster tells themselves]a vote for obama.
That statement works exactly the same way if you reverse the candidate names. Any vote not for Obama is [no matter what the vote caster tells themselves] a vote for Romney. Of course, the answer isn't known in advance, but a "not vote" is arguably accepting the results, and therefore is a vote for whoever the winner ends up being.