Every time I hear some whiney Red Sox fan bitch about the Yankees fan-base, they seem to forget that while Boston itself is not an enormous city, the Sox get every baseball fan north of Stamford. Yes, the NYC metro area is huge, but the Yanks share it with the Mets. If the Sox can not keep up financially, they ought to tear down that 30-seat eye-sore they call a ballpark and build something more practical.
The Yankees fanbase is based more on their long history of success than on geographical location.
The Cubs and Sox are the opposite - they are the two sorriest franchises in baseball and their enormous fanbases come from geography.
Go suck an egg cream. You...Yankee's fan you. =;^)