I don't follow gaming news anywhere near as much as I used to (whereas I used to have enough time to play a game a month, I now have enough time to play about 2 games a year,) but I just got a theory on why this game was delayed when I read this in an article:
Only one GamePad comes with each unit, and the controllers are apparently too expensive at this time to sell separately. (Nintendo reps say that no games available at launch can use two GamePads; when a Wii U game comes out that could take advantage of two GamePads, Nintendo will offer additional GamePads for sale.)
My theory: this game has been delayed because they want it to be able to use two gamepads. They don't want to release the game before they start selling gamepads separately, as that would piss people off who buy the game at launch expecting to play it with two players.
It has nothing to do with quality issues. There's nothing they want to spend an extra few months on. They just want to avoid backlash from releasing a game that you won't be able to take full advantage of all the advertised features of for a few months.
I think that, for once, Nintendo doesn't want to crowd the launch with their own games. Their 1st party titles tend to out sell 3rd party titles.
The average consumer is probably willing to buy three or four games at launch. It seems as those Nintendo has gone out of their way to ONLY release two developed by them: NSMBU, and Nintendo Land. Nintendo Land is there because it's an easy way to show off all of the new features of the Wii U, and is a bit less transparent than Wii Sports, and more of a crowd-pleaser, by featuring Nintendo's biggest franchises. NSMBU is there because it was a little weird when the Wii (1) launch without a Mario game.
If Nintendo piled-on the titles with Mario, Pikmin, Zelda, Metroid, (ect.), then very few of the other titles would get noticed. Just Dance 4 might not sell as well if it has heavy-hitting competition. If 3rd party games do not sell well at launch, then 3rd party developers are definitely going to be less likely to publish on that platform. It sets a bad tone for future releases. Nintendo may be putting very few of it's own games out so that the others will sell more, get better numbers, and be more likely to release on their platform in the future.
It's a strategy. The Wii (1) lacked a strong 3rd party support; most of the games that sold well for it were developed by Nintendo, directly. The only other company that did well on releasing games for the Wii was Ubisoft with Raving Rabbids and Just Dance; this is also reflected in Ubisoft VERY strong launch lineup for the Wii U.
The lack of other companies to support the Wii (1) was a weakness. If Nintendo holds back on it's own software, that may help it further down the line.
Although I'm sure Nintendo EAD is capably of completing Pikmin 3 by now, I would think that they would be smart enough to use this delay wisely. Perhaps to fine-tune parts of the game that could have otherwise been rushed. They are well aware of Nintendo's planning ahead of time. They know that there is no need to print the game to disc quite yet; and until then, they are able to keep editing it.