[WingsToDiscovery]

Well the full name of Rugby is "Rugby Football." Due to alterations in the sport (creating American football) there needed to be some kind of disambiguation between Football (soccer) and this new sport. "Football" was chosen for the new sport, and "Soccer" was chosen as being derived from the full name of Soccer, "Association Football." That's basically why America has that difference. TokusatsuFan basically reiterated what I believe; that there just happens to be more influence on American English when Katakana-izing things.