I do agree that Boston has become more popular in recent years but that wasn't always the case. As a long suffering Red Sox fan I do get a kick out of the Johnny come latelies especially when I quiz them on years past. I am a born and bred Tennesse boy basically chose the Sox as my team because my brother was and is a Yankee fan.
But you got to remember....the Braves weren't born in Atlanta! Most oldtimers around here were either Reds or Cardinals fans. I remember many nights listening to the Cardinals and the Red Sox on the radio with my dad. He was a fan of both.
But you are right about the Yanks and Sox.....but the Yanks have always been that way.