Twice a year, the Audit Bureau of Circulations reports the number of subscribers to each major newspaper. The Awl collected their data going back 20 years for the Wall Street Journal, New York Times, LA Times, Washington Post, Daily News, and New York Post, and drew this really cool graph (after the jump). The WSJ is up over two decades. The New York Post is unchanged. The NYT sort of bobs around. Everybody else follows the general trajectory of a ball tossed off a 50-story building.
Stephen Dubner said at Monday's SuperFreakonomics event that decades ago, journalists assumed that if something went reported in the Washington Post or the New York Times, other papers were reluctant to follow because they assumed the story had been optimally publicized. Today the Wall Street Journal's circulation (including paying online readers) is more than the Washington Post and the New York Times combined.