As you probably know, many college teams play for various bowl trophies, eg the Orange Bowl, the Rose Bowl. The professional game had to be bigger and better so it was called 'Super' Bowl. It was called the Superbowl after the first two head-to-head games between the (formerly rival) professional leagues: the American and the National (Superbowls I and II weren't officially known by that name at the time).
(With a bit of luck, we'll get to see a UK based team win the Superbowl in my lifetime
)
The World Series in baseball was orginally called "The Championship of the United States" but several newspapers started calling the 1884 Providence Grays "the World Champions" and the name stuck. The first time the championship was officially called the World Series was in 1903. Blame the media for that one!