It is only a slight exaggeration to say that success in the regular season in determined by the back end of pitching rotations, but that in the playoffs these pitchers barely matter.  Successful regular season teams frequently have strong number four and five starters who, while not expected to shut down opposing offenses, can keep their team in the game.  Teams with genuinely good four and five starters in the regular season usually are very difficult to beat over the course of a long season.  Similarly, good offenses which can consistently beat up on the back ends of opposing rotations can give their teams a real advantage in reaching the post-season.