According to a Sports Hochi tweet, both Ichiro Suzuki and Hiroki Kuroda have decided to sit out the 2013 World Baseball Classic.  Source: Sports Hochi tweet 11/19/2012

Additionally, it seems Ichiro never really considered playing in the third WBC after playing in the first two.

"After the second tournament ended in 2009, I never thought about playing in the 3rd one.  That feeling has not changed and that is my decision."

Source: Nikkan Sports 11/19/2012

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UPDATE @ 6:19pm - Kuroda's comment:

"It is an honor to be invited to play for Japan and I am thankful for it.  However, I felt it would be difficult to prepare myself to the max by March, considering the number of games and innings I pitched this past season.  I feel bad that I could not lend my support to Koji Yamamoto."

Source: Daily Sports 11/19/2012