Running in the area of 14-15 million viewers...the rest of the population (300 million) ignored it. Outside of Boston (spit) and St. Louis, no one seemed interested.
A byproduct of there being so many levels of playoffs is that nobody but the fans in two cities are interested by the end. Everyone else is baseballed out by then. Same goes for hockey and basketball, IMO. That is what makes the super bowl and the NFL so special. Single games matter so much more.