Well, honestly, I usually don't care much to know the specifics of why a game is delayed. It doesn't matter to me, so far as I know it's to add polish. However, this, to me, is too unusual. It doesn't make sense. There's no other big title being released at the same time, there's been much fanfare online about this day, and as far as we can tell, at least the Japanese version of the game is completely finished, meaning no new content will be added. Nintendo has known how much text is in the game, and we've seen in the Dojo that text is being translated basically simultaneously with the Japanese version into several languages, including the two most common languages used in North America. I'll be disappointed this time if the game is delayed here but not in Japan, because as far as I can tell, there's no reason for it. They wouldn't just add one character in to the US version, Sakurai would want everyone to get the same experience.
The only thing I can think of is censorship issues, but Sakurai, I believe, was offered full control of the games, and would probably just want the game to take a higher rating, rather than censor it. Anyone have any ideas as to why? It just makes no sense at all to me!