To be honest, I think this is an easier situation to reverse than most. For example, does anybody remember the CC Sabathia game against the Pirates a few years ago? There was a questionable call in the middle of the game as to whether or not Andy LaRoche got a base hit or reached on a Sabathia error. While I think that the play was clearly an error, it was ruled a base hit and that was the only hit of the game for the Pirates. Without that hit, Sabathia would have had a no-hitter. The Brewers got it reviewed, but not reversed.
Unlike that situation, the evidence is clear that the batter is out. Even more important, this was the very last out. So if the call was correct, then you can guarantee a perfect game, whereas in Sabathia's case, who knows how the rest of the game would have panned out if the call was an error. In this case, Galarraga pitched with the same pressure of a perfect game, and if the call was made correctly, then the game is over and it's a perfect game. It seems like it could actually be a perfect game. I won't get my hopes up that Selig would do the right thing, but it's now or never here.