IF you're refering to Ulver and Marks TOAW scenario, the victim doesn't have a chance to redeploy it's army before being attacked either. The one turn delay in the house rules is because the Theater Option that releases the victims army isn't executed until the begining of the next axis turn. The order of events is: turn N: axis player selects the declare war theater option, and ends his turn without crossing the border or attacking. The allied player does his turn N, but doesn't have any indication that the axis has declared war, and is unable to move the victims army. Turn N+1: the Event Engine removes the yellowbars allowing the victims army to be moved. Axis turn begins and the axis player attacks often siezing the capital and ignoring the victims other forces. Then the allied player opens his turn and sees in the news/replay that the axis has declared war on victim and possibly has taken the capital. If the capital is in axis control the allied player then has a single turn to retake it before the victims armys disband. In the case of minor countries, the allied player rarely can take the capital back becuase paratroops were used to block the retreat of the defenders in the capital, resulting in them evaporating instead of withdrawing. The paratroops are typically dug in, and can typically hold out long enough to prevent any troops in the vicinity from being able to counter attack the force in the capital until there's too little time left in the turn for them to liberate it.
THe one turn delay is to allow the allied player to be able to counter attack the same turn as the axis invasion begins.