Generally speaking, working for "exposure" is an empty promise because that "exposure" doesn't actually net you anything. This hearkens to all that stuff you always read about never working for free and devaluing your profession when you give away work, etc., etc.
The Super Bowl, however, is an exception to this, because the Super Bowl is arguably the most watched entertainment program in the US every single year. Working for "exposure" at an event on the level of the Super Bowl translates into real monetary gain. The kind of attention you get by working as an entertainer during the Super Bowl halftime show is higher than any other concert you could ever perform.