It's a savy business move, especially from a marketing perspective as the high inital sales figures that were expected will be further exacerbated by the Holiday rush. After all, the day after Thanksgiving is the biggest shopping day of the year and any outlet who offers it will be swamped if the release co-incides very closely. Then add that those incredible initial sales figures will in all likelyhood stimulate mainstream media coverage that it otherwise may not have garnered and the publicity alone would be worth millions were it paid for. Of course it may just be a delay in order to fine tune it as has been said but it would make sense for those reasons as well.