These polls show the candidates as individuals, yet you will vote for a ticket. The choice of VP candidate for each party may change the polls and indeed the outcome. It doesn't mean a thing that the VP does little but preside over the Senate and is a tie breaker. People see the ticket as a pairing. Some may even think of the possibility while voting that the VP may become President. That would be either through the incapacitation or death of the President, or the fact that many carry the VP spot into candidacy in a future election.
When people say Obama won't win, I wonder if his choice of VP will change that. If he did pick Hillary, would her odds improve, or drag down the ticket. I think a lot of people talk one way and vote another. I see a lot of women throwing a vote at Hillary when they get into the booth. They may not tell hubby that.
Would you call that a closet vote?