ESPN certainly plays a major role, as the main nationwide sports-hype machine. keep in mind, though, that ESPN is in the business of making money, not ensuring that every team gets equal coverage.
they cover and show the teams that they think will generate the most interest. MLB deserves most of the blame for this (heavy yankee-sox coverage). often, the stars end up in NY and BOS where the larger payrolls are.
maybe the ESPN had more coverage of teams like KC and OAK back in the 80's b/c OAK had some monster teams and that was a time when KC could keep a 1st ballot HOFer on their roster for his entire career? blame MLB, not east coast bias.
it could be a regional bias that causes so much patriot coverage. or it could be that they won 3 SBs, made a run at 19-0, and had a major cheating scandal.
in the NBA, ESPN has no problem shifting heavy coverage to the lakers, spurs, suns, and mavericks over the past few years.
ESPN has no problem going overboard covering the packers and favre b/c people find them interesting.
they also have no problem hyping michigan-ohio state in football.
i'm not a yankees or red sox fan, but i watch when they play b/c it's interesting baseball.
i do not think ESPN covers them so much simply b/c they are located in connecticut.