Okay either there is income, education, racial links to these results. Or the Obama supporters moved to the Southern part of the county in the past 4 years. The latter is very unlikely though, so I assume the former.
Combination of factors likely, one key one being transplants. South Charlotte has a TON of New Yorker's and other transplants (my parents are just over the border in the tip of Lancaster).
Its pretty much the same thing in portions of Wake. Cary is a prime example. Its not quite as Republican as South Charlotte (more of a swing area), and was very strongly against the Amendment,
