I'm not completely sure was it planned, but Stringer Bell was a character who attended community college, got his food from an organic food market, didn't want to be connected with the street. Almost like "coastal elite" and the New York slang would make sense there.
Strangely, most of the significant characters in the drug trade are missing a Baltimore accent. I'm not really sure what accent Idris Elba is going for though it sounds vaguely New York City, while Method Man clearly sounds like a New Yorker when his character is from Baltimore. Wood Harris, who played Stringer's partner Avon Barksdale, sounds like he's from Chicago. The only ones speaking in a Baltimore accent are Proposition Joe, Slim Charles, and Snoop Pearson.