I disagree with this completely. In my opinion, if you are in a close race that gets decided by a handful of games, a single move can be enough to put you over the top, and it doesn't have to be a move that gets you a star player that costs you the farm. In many of these close games, a key hit can change the outcome. A good inning from a bullpen guy can win you a game. Will the acquired guy be directly responsible for the additional victories? No, he might not even get one game winning hit, but the team will be improved. If we had plugged the black hole that is Kevin Cash when Varitek first got injured, maybe the guy in front or in back of him gets pitched to differently. With Cash in the lineup, you could essentially pitch around the two guys in front of him, because he can't get the ball out of the infield. I'm just using Cash as an example, but I firmly believe that a single acquisition could make the difference. One player can change the whole dynamic of a game and a team.
Do you remember 2006? Yes we had a ton of injuries and the team fell apart, but the Yankees were not in any better shape in late July 2006. They got Abreu, and that guy dismantled us in the 5 game series at Fenway in the middle of August knocking the Sox from 1 1/2 games back to 6 1/2 games back in a single series. He was a big difference maker, and he did not cost the Yanks their farm system.