Relievers are typically not worth a whole lot in terms of WAR. In addition to them not pitching as many innings, it is not as difficult to replace them. If a closer gets injured, he will likely be replaced by the 8th inning guy who is typically almost as good. The reliever that is called up from the minors does not go into the closer's role, but instead becomes the #8 reliever. Because of this, the replacement level value of relief pitchers is not as high as it is for starting pitchers or position players.