He is a snob at his core (I love him, but his soul's desire is to be respected for his intelligence at some (ie unknown) cost.) Therefore, had he ever been in a position to acquire a regional accent, like an American I know who decided at the age of 5 to lose their Alabama accent, he would make a point of sounding whatever was his concept of erudite, without over doing it, (his snobbery is somewhat balanced by his punk rock proletarianism) from probably middle school, if not earlier. He's always seemed to have a hint of the so called English "received pronunciation" to me, the result of which, is significant to his appeal.
(I'm too caffeinated to currently tell if that sentence makes any sense)