Looking at the 2008-2012 swing, it looks like Southern Georgia stayed relatively the same, but Northern Georgia trended strongly to the Republican, so this new and mountainless Georgia might have been won by the same percentage in 2012 as 2008.
Looking at that, yeah, you're probably right. It is possible that Fulton's diff in swing to Romney versus the swings for Obama in the south might have allowed Romney to gain a point over McCain; there's only 3 Obama swing counties on there in "New Georgia" that have more than 100k people.