Yes, that's part of it. This might sound stupid, but I think part of the Republicans' problem is that they have too many influential figures with southern accents. That's a turn-off for the rest of the country.
As George Voinovich once said, "It's the Southerners. They get on TV and go 'errrr, errrrr.' People hear them and say, 'These people, they're Southerners. The party's being taken over by Southerners. What the hell they got to do with Ohio?' "
Regions with southern culture don't exist exclusively in the South and there are parts of the South that aren't really southern. More former than the latter.