Shigeru Miyamoto said it's feasible the game could have been released last Christmas, but that plan wouldn't have been the best move for its quality:
If we'd only been thinking about what was most convenient for the company when we made this new game The Legend of Zelda: Skyward Sword, we probably would have put a half-finished product on sale last Christmas by saying that we have managed to make it on time just because it was the order from the company.
Miyamoto and Nintendo president Satoru Iwata both felt that releasing the game before it was ready would have been a mad move, Miyamoto revealing the game went through six months of polishing to get it up to standard:
Because the game we were making was so huge, we needed to work that hard on it. Otherwise it would have felt like a waste. We spent so much time making a really good game and it came out so well that it would have been a waste not to make sure that it was really polished.
Miyamoto is known for saying that "a delayed game is eventually good, but a bad game is bad for ever", and while we doubt that's the case with Skyward Sword, considering the game's stellar scores — including a well-deserved 10/10 in our own The Legend of Zelda: Skyward Sword review — the extra delay paid off.