Depends where you live. For example, in Boston almost every game is broadcasted on TV. However, where I live, in Maryland I rarely get any Sox games so I bought the MLB extra innings package.
It wouldn't surprise me if there is people who watch every game, but there is no way I can. It's not that I don't want too, its that I have other things to do, such as work, hang with friends and etc. That being said, I probably still watch about 100 games a year (not including playoffs.)