Despite ostensibly bringing it up I feel that no "genetic" explanation is really meaningful. Obviously there's a hereditary influence, but I doubt and do not care for magical traits obeying hard fast rules.
I can dig this but think there's something better out there along this theme.2 things.
Has "My Little Pony XLIX: Shipping is Magic" already been used as thread title, given the generator... right? right?
*rolling weed passes by*
I can't, at least when I lived in San Diego for a year. Then again I probably have higher standards for having an actual accent. I suppose liguistists need something to amuse themselves with though. I think I read something once that whether you say soda or pop is considered important for accents, which I find ridiculous. (Yes I find people saying pop bizzare but that's not an accent)
They are also pretty rare, or at least only apply to much smaller parts of then media would have you believe.