I also found this picture interesting. I "liked" the show The Closer way back when so I always get their updates. The final episode was last night (it was a good one), so the facebook page had this up. It's a riff on the main character's Southern accent (she says "thank you" with a smile a lot to people on the show). Brenda (Kyra Sedgwick) is a transplant from Atlanta to Los Angeles.
Of course, they changed the spelling. Why?
Why isn't this spelled "thank you" and the same utterance from Angelenos spelled "thank yoo"? Or better yet, why don't you just spell all of them "thank you"?
When you read written Southern speech you see "ya'll" a lot too, but that's actually a different word, not just a different way of pronouncing the same word.
Is it the normalization of a particular region relative to another region? Southerners have long been considered the Other in America. To a large extent it's a numbers game of course too.
But again, an interesting picture.
I'm always a little disappointed when I hear Sedgwick speak with her actual accent, myself. I only sound mildly Southern - and that waxes and wanes. Northern Virginia is a melting pot so I never picked up a particularly distinctive accent. Actually my most distinctive pronunciations are Baltimorean, where half my family is from.