The New York Times passes along a bit of truth:
In spite of clichés about Nascar dads and Walmart moms, the actual share of voters nationally who are up for grabs is probably between just 3 percent and 5 percent in this election, polling experts say. The Obama and Romney campaigns are expected to spend on the order of $2 billion, in part to try to sway this tiny share of the electorate.
....A decline in swing voters would help explain why Mr. Obama and Mr. Romney have stayed within just a few points of each other, across many polls, despite months of a gyrating economy and attacks on both candidates.
It's also important to mobilize your base and get them out to the polls, so it's not as if appealing to this tiny number of swing voters is literally the only thing presidential candidates care about. Still, it's most of what they care about. What's more, they don't even care about all the swing voters, just the ones in swing states. If you were to break down the actual number of human beings the two campaigns are really truly trying to persuade, it might be no more than 2% of the population. All the rest of us are just bystanders.