There were six North Carolina counties where Barack Obama's performance was more than a point worse than John Kerry's in 2004: Cherokee, Clay, and Graham in the west, Camden, Columbus, and Richmond in the east.
Three of those I have a pretty easy explanation for: they didn't see the same campaign the rest of North Carolina did because they're in media markets in other states. Cherokee County is in the Chattanooga market, Clay County is in the Atlanta market, and Camden County is in the Norfolk market. Camden County probably still saw a lot of ads since Virginia was also a swing state, but Cherokee and Clay are likely to have seen far less of Obama's message than other places in the state.
The other ones I don't really know what to say. It's easy to chock it up to racism but Columbus and Richmond Counties each have black populations over 30% so it seems like increased turnout there should have resulted in an Obama improvement. Why would white voters in Columbus County be more likely to vote against Obama because of his race than those in Bladen County? Why would that be more of a problem in Richmond than in Montgomery? I don't know the answer.
The other thing these counties all have in common is that they're on the border. Was the Obama ground game weaker in those places?
Ultimately it doesn't matter but I'd be interested to know more about what happened in those places.