NBA has 16 unique franchises with championships since the NBA-ABA merger(1976), where as the NHL has 19 in the Stanley Cup era(1915). NFL has 20 different teams with championships in the Super Bowl era(1966). Just added their 20th this year(Eagles). So parity isn't really a problem. But one NBA team can be lifted for years by one superstar(Russell, Jordan, Duncan etc) and stay in contention for much longer than an NFL or NHL team, due to there only being 5 players on the court and the fact that the superstar plays both ways.