Eaton's exit was possible because the Phillies will need only four starters in their series with Colorado. Cole Hamels and Kyle Kendrick will pitch the first two games of the series in Philadelphia, with Kyle Lohse available for long relief if needed. If Lohse isn't needed, he'll start Game Four, with Jamie Moyer pitching in Game Three, while Hamels would return for the series finale, if needed.
Geoff Geary, who is suffering from a mild elbow strain, was also left off the roster in favor of Clay Condrey. It's possible that Geary could return if the Phillies advance to the National League Championship Series. A name from the past might also be added to the roster for the NL Championship Series as he recovers from a right shoulder injury that put him on the DL a couple months ago.
Chris Coste, who was a surprise omission from the Phillies Opening Day roster, is on the post-season roster. He would have likely been there anyway, but is now especially important with catcher Carlos Ruiz suffering with a sore arm following getting hit by pitches in two of the tree games against Washington this past weekend. It will likely be a game time decision whether Ruiz will start in the first game of the series Wednesday afternoon.
Teams can readjust their post-season roster after both the Division Series and League Championship Series.