I suspect the problem, as Quovatis is getting at, is that the replays we already have are not actually replays. They seem to be re-enactments of the same or very similar commands that are given out by the attacker, but either because of randomized behavior or minuscule timing or position errors, the results are never exactly the same as the original attack, and in fact sometimes can be dramatically different in terms of loot taken, etc.
Still I would rather have bad replays than no replays....