A lot of people are very angry about the situation. There really is no reason to delay a game just so it could come to all platforms at once. The game was completed, too. Plus, it'll get overshadowed by other big games in September 2013 and Holiday 2013. It's a dumb move. Even the developer was upset about it, too.
Even so, Ubisoft promised an exclusive demo for Wii U owners soon.