According to the Copyright Law of the United States of America, it is illegal to watch the Super Bowl on a television larger than 55 inches...under certain circumstances.  See for yourself in U.S. Code, Title 17, Chapter 1, section 110.

Don't worry, the "NFL Police" won't bother you at your home for watching it on your 65" Plasma! The law mainly applies to "food service and drinking establishments" of a certain square footage.