Quickest way to prove it is checking K-Rod's debut date on baseballreference.com He made his major league debut on 9/18 then was on the postseason roster. I can't off the top of my head think of the guy who was on the 60 day DL that he replaced, but I want to say it was some nobody who may have never even wound up playing in the majors. K-Rod may not have even been on the 40 man as of 9/1(though he was in the organization), I'm hazy on that part. The logic behind it is that postseason rosters are supposed to be locked in on 8/31 to prevent a guy playing in the playoffs that wasn't really a part of the team for the most part. Teams discovered loopholes because obviously if one of the guys on the 25 man roster got hurt, he would be replaced by somebody else from the 40 man come October. Additionally, if you have a guy on the 15 day DL that you want on your postseason roster, you'd put him on there. Let's say he relapses and isn't healthy enough for postseason play, you then have to replace him. So the loophole was taken to the extreme, and occasionally a team will ensure a minor leaguer will spend the season on the major league 60 day DL to allow for manuevering in order to clear space should they so need it. For example, having Pagan on the playoff roster(In place of Pignatiello) in addition to every position player on the current 25 man would allow the Cubs to go down to 11 pitchers for the playoffs, which is really all a team needs come postseason.