[Ref'sProudPapa]

I saw a documentary once (not about replay) that showed an actual replay review in Fenway park. It was a single screen in the hallway leading from the home dugout to the locker rooms, just in the middle of the wall. One umpire stays on the field. One umpire stays in the hallway keeping away cameras and players and team reps, so only two actually do the review -- presumably the crew chief and whomever's call it was if those are different people.

The tv was kept in one of those metal boxes on the wall like your electrical panel. The screen was about the size of one of those dvd screens on the back of a car seat in a mini-van.

The NHL system seems to work pretty well and the set up in Toronto is impressive. But I guess one difference is that NHL arenas don't have ground rules and all playing areas are uniform. Whether or not the puck crossed the line, or was kicked in, is the same in Phoenix as it is in Winnipeg, except for maybe slight camera placement differences. MLB crews each series go over pretty carefully the ground rules of each stadium and have them in mind when they are doing reviews. They are also there, live, in the park, and so can see things that might not be apparent on tv -- for example how deep a gap is between a fence and the stands. Also, on any given night in the NHL, Toronto will be called upon for at least a couple of reviews. You can go weeks in MLB without a review. Having a war room, with a dedicated crew versed in the ground rules of 30 stadiums seems a bit infeasible. I guess I'm leaning toward centralized review if the alternative is that crazy procedure I saw in the Fenway documentary. But, to go along the lines of the OP's question, I don't think centralized review is as obvious in baseball as it seems.

One thing I'd add is that we all seem to take as granted -- largely from the NFL experience -- that the call in the field have primacy unless the video evidence is overwhelming, and from Hernandez's supposed comments yesterday that seems to be the rule in baseball as well. Everyone acts like this is an obviously correct method of using video. I disagree. Once you make the decision to go to video, go to video. If video is not adequate to make a call, that's one thing. But if you have the tape, forget what happened on the field, and make your call based on the video just like you make your call on the field. If you are truly in equipoise after seeing the video, fine, the tie goes to the call on the field. But the circumstances in which reviewers and the league think this should be the case seem to be a very significant band, not a very narrow one, as I think should be the case.