Maybe we can, if we're not too greedy about it. As a voter, you are a little like A, B, C, D, or E in the above diagram. Suppose I am A. I get a little bit of the credit for holding up F even though it's true that if A were removed, F would still be aloft. A is not "the deciding vote" for F remaining aloft, but still contributes to F's elevation. Surely you have to say A is helping keep up F. If you say A isn't contributing, you'll have to say the same about each of the other blocks. Then you'll have to generalize and say none of the blocks are holding up F--which is ludicrous.
In the block situation, the weight of F is resting on all five lower blocks, so A gets some credit, even though A could be removed without F falling down. I'm suggesting voting is like that. My vote helped Obama get re-elected, even though it's true that he won by a couple of million votes, so if I hadn't voted, he still would have been elected. The analogy isn't perfect, but I think there's something to it. If you say my vote didn't help, you're going to have to say the same thing about any other vote for Obama. You'll again have to generalize and say none of the voters made him win--which is ludicrous. The blocks all help, even if there are more than needed. The voters all help the winning candidate, even if there are more than needed.
So I say each Obama-voter can take pride in causing Obama to win yesterday, even if it's true that none of us cast the deciding vote.* We did have good reason to vote: in order to be causes of his winning. And if you voted for Romney? You get to be proud too. There was a reasonable chance your vote would be part of the cause of Romney winning, even if there was virtually no chance you would cast the deciding vote.
* Thanks to the first comment, I need to clarify. I'm ignoring the US electoral college system here. Given the electoral college system, it really is true that a voter in a very red state like mine--Texas--couldn't help Obama win. But on the other hand, we all think it was important for Obama to win the popular vote, nationally, and we in Texas did help him do that (despite not casting the deciding vote)--or so I am arguing.