The catcher is by far the most important non-pitcher on the field. There are many catchers who can't hit. There are some hitters who can catch, but there are few catchers who can hit, and in the entire history of the game there have been hardly any very good catchers who are very good hitters. Not only was Mauer probably the best player in baseball in 2009, but his 2009 season was probably one of the top 25 or so most valuable seasons in the history of the game.