Heheh, no problem I had to look it up because I didn't know.
Looks like The Who had a tour planned for 2010 after their Superbowl performance (not sure it materialized though), and Tom Petty started a north American tour after Super Bowl XLII.
Right so even if there is no new album to promote, there is usually a new tour that is being promoted by making an appearance on the SB. I mean, what better way to promote your new world tour than by performing during a sporting event that is watched by a couple hundred million people worldwide?