I just don't get it, that's a huge delay, and one they should've seen coming and eased into.
I wonder if this isn't a case of the game being "bad," per se, but someone making demands after seeing some things he or she didn't agree with, or think typifies Zelda. For example, we know Miyamoto has had his strong opinions about the series (such as feeling that it was getting too "adult" when Link started to wear an earring in OoT and such, and in response jerked the series back in the other direction with Wind Waker), and I thought he was trying to sit this one out, yet right there in the news, his name gets top-billing. Maybe he didn't like the plot or something about the game, and has demanded that a certain portion or portions be significantly altered.
I don't know, that game just looks incredibly far along to suddenly need an additional 4-5 months at least, and the fact they hadn't been warning press and such that the game may slip from the previously predicted release date suggests that the decision was sudden, and unrelated to resource creation or testing.