The way I phrased the question, it sounds like a bad thing. In fact, these players can be considered some of the most valuable players to their teams. What we're looking at here is the winning percentage of the team when a player is in the starting lineup compared to when he's out of the lineup for an extended period due to injury (or any other reason).

For example, Scott Podsednik has missed 35 games for the White Sox this year. Their record in those games is 18-17 for a .514 winning percentage. That's a percentage barely above .500 for the team with the best record in the American League. But when he's in the lineup, the ChiSox have posted a 69-38 record for a .645 winning percentage. That's an increase of 131 percentage points. Impressive. But there are eight guys better then Pods.