Think how long we have been told/forcefed that every American is racist. So much support is out of "white guilt" while plenty more is due to his "cool,young,hip" factor.
I have always lived in the deep south and was educated in public de-segregated schools. I recently realized that plenty of people (typically over the age of 45, or so) grew up in a racist atmosphere, and now have incredible guilt from their earlier opinions. It makes them "feel good" to vote for Obama - the same feeling they get when they drive (use gas) to drop off a few plastic grocery bags at the recycling location.
I think you’re right about the guilt. Maybe people are just saying one thing to pollsters and will vote another.
Either way this election goes, we are in for a rough time.