Players come and go during the MLB offseason as they sign with new teams. They also get dealt away by their teams in an effort to bring in more talent.
They may not think that they miss them right now, but major league teams will miss some players that they lost this winter. They could have been big pieces of their teams in 2012.
Some team's lost superstars while others traded away promising young prospects. Either way, the teams made a decision and if these players perform well then they will certainly be missed.