From Max Read's fantastic article nitpicking the inconsistencies in Game of Thrones' deployment of regional British accents:

"The show has dragons, who cares if the accents don't match?": Well, first of all, I care. Second of all, the cornerstone of science fiction and fantasy fandom is nitpicking. Third of all, the fact that Game of Thrones doesn't take place within our collectively agreed-upon reality doesn't release it from its responsibility to verisimilitude or the maintenance of internal consistency within its own systems.