For the sake of conversation, I'm going to say that Nintendo shouldn't really do this. You all bring up great points, and I actually completely agree with
Turo602 and
VanitasXII in terms of reasoning behind their opinion. But while they say things about having achievements for
Skyward Sword and how gamers are competitive, it really isn't in Nintendo's nature to have achievements. I mean sure, Super Smash Bros. Brawl had "achievements" in a sense of you unlocked things for completely specific tasks, but other than that Nintendo really isn't the type of company to penalize casual from hardcore gamers with achievements. <-- What I mean by that is having achievements would make casual gamers, who just play to play, feel penalized compared to hardcore players, who would be willing to collect every achievement.
Nintendo is a company known for being family-orientated and their also known for connecting with casual AND hardcore players. Having an achievement system would be fun, but it would also pull Nintendo away from what they're known for.
/minirant.