Arbitrarily because Iwakuma just hit the 50 start mark this year.
So what has Iwakuma done since he became a full-time starter? Only given his team Hall of Fame caliber outings in over 50 starts. Granted, he has nowhere near the track record in MLB as many starting pitchers enshrined in Cooperstown. But for what service he has given the Mariners, he irrefutably has deserved to be paid like a Tanaka. Since 1920 for starting pitchers who qualify with a minimum of 50 MLB starts, Iwakuma ranks first in earned run average with 2.58 mark. That ranking covers a span of nearly the last century of baseball in America. There is no one above him on that prestigious list. Here are some of the names he has bested so far in his career:
Clayton Kershaw (2.64)
Hoyt Wilhelm (2.68)
Whitey Ford (2.71)
Sandy Koufax (2.71)
Tom Seaver (2.86)
Read more at http://www.rantsports.com/mlb/2014/05/21/seattle-mariners-hisashi-iwakuma-silently-rewriting-record-books/?k4IrU8PF0DdJbTYI.99