I heard quite a bit of different accents in XII. Most of the characters that came from Archadia had british or western european accents; not forget about Fran and Balthier as well. Many of the voice actors in War of the Lions had accents.

Though outside of the Ivalice Alliance I do agree that many of the characters in many of the FF games have a more northern or even northeastern american accent. Or as some from the deep south in the U.S put it, the voice actors typically have very yankee accents. I suppose the reason most of the voice work in the series is like that is because I imagine most of the voice actors are from the northern half of the U.S. However thats just a guess.