When the Super Bowl ends nobody regrets that it isn't a best of three, five, or seven series. When the NCAA Tournament produces upsets, no one suggests that Lehigh “has put themselves in a good position to eliminate Duke.” The drama that comes from a winner take all sporting event is unparalleled and that's why the notion that “game seven” is the best phrase in sports is ridiculous. Every sport could have a game seven, or a one and done, every season, but the bottom line gets in the way.
The reason we have playoff series' in most sports is simple. The more games that you play, the more revenue that you can produce. By having the playoffs last two months you extend the season for television and radio revenue in addition to ticket cost, concessions, and apparel. Why did the NBA expand from a best of five first round to best of seven in 2003? Money. Why has baseball shifted from just division champs making the playoffs, to having a wild card, and then establishing a second wild card? Money.
While baseball is played in groups of two, three, and four games throughout the regular season, and pitching rotations are geared towards winning the majority of games over a long season or relatively short series, baseball has proven that they don't really care about anything other than cash. Teams now play 162 games to have a one game wild card playoff. The only sport that plays series' all season long has two one and done games because a) they want to maximize revenue by having extra playoff games, but b) the season can't go any further without the risk of the World Series being snowed out.
As for basketball and hockey, understandably as the leagues have grown more teams deserve to make the postseason. However, why reward mediocrity? Sixteen of 30 NBA teams make the playoffs. Congratulations Milwaukee Bucks, you went 38-44 but were better than the Sixers who went 11-30 on the road, and the Raptors who won their final five games to get within 14 games of .500, you get to make the playoffs.
The NHL also allows 16 of 30 teams to make the playoffs. One could argue that since the eighth seed in the west, Los Angeles, won the 2012 Stanley Cup Finals, the system is working. Perhaps the regular season doesn't matter enough when you can put together a six game winning streak during mid March and it will be good enough to offset an average rest of the year and secure a birth in the tournament.
Game seven of the NBA finals was exciting and filled with drama. It will be lost in history because game six was one of the great games ever played. That doesn't happen in sports that don't create series.
The point is not that we should get rid of playoff series. They are here to stay and give sports fans the nail biting tension that they love for weeks if not months on end. What needs to be recognized is that what makes game seven so great is all of the cliches: winner take all, do or die, backs against the wall, win or go home, for all of the marbles, and so forth. The NCAA Tournament and NFL create this scenario every season. Game seven's are somewhat rare, and have great significance. However, they frequently pale in comparison to a previous game in the series, and exist more for financial gain than to provide more entertainment. For the team leading a series three games to two, game six is where you want things to end, and even the clinching fourth victory of a series is no more important than the previous three wins. Game seven is great; just imagine what a decisive game nine or 11 will feel like.