monopoly definition

[tklaundry@juno.com]

I'd like to throw this out to see where it goes.  
There was a move recently in Congress (a move that never got off the ground) to repeal the exemption that Major League Baseball has from the Anti-Trust laws of the U-S. I as a layman can only assume that MLB meets the requirements of violating those laws without that exemption, otherwise why would it exist?  So here's the question.  If MLB is considered a monopoly then what prevents the same standards from being imposed on corporations that own most if not all the major stations in the major markets?  
Here are some of the specific issues.  There are 28? MLB teams in the
U-S each with different and seperate owners,  in the Major markets the same half dozen or so companies own a majority of the radio broadcast signals.   MLB appears to be a monopoly even though there are hundres of professional baseball teams outside of the Majors, so why wouldn't the same standards apply when dealing with the Major Market Broadcast markets?
Just something to chew on.
DF