If MLB wants to prevent millions of people from buying its product, that's its decision. It may be dumb, but presumably (I know with Bud Selig in charge, this is a leap) MLB is making a decision in its best interest.
Perhaps Chevrolet would sell more cars if it didn't sell exclusively to Chevrolet dealers, but it doesn't. Why? Because Chevrolet feels that if it has exclusive dealers, those dealers will work to promote the Chevy brand and reduce intrabrand competition and promote interbrand competition.
Like it or not, there are only so many sports entertainment dollars to go around, and as much as you'd like to separate baseball into its own individual market, it's not. People don't view baseball that way; rather, it's simply a sport, on which they will choose or not choose to spend money based on their entertainment budget. MLB, in a very real way, competes for money from NASCAR and the NFL and the NBA, and if MLB thinks that an exclusive dealings contract with DirecTV will help it better position itself for the limited entertainment dollar of Americans, then who am I to question? Who is John Kerry to question?
Well, as a lifelong sports fan, I disagree strongly with your statement. I don't give a damn about NASCAR, basketball, or hockey, and there is a limited overlap between MLB and the NFL. People do, on the average, separate the sports into their own compartments.