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
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