The Wii U is going to have an achievement system, according to Nintendo, but adding them to games will be the developer's choice. Nintendo of America president Reggie Fils-Aime told Kotaku that a system will be in place, but "once you start getting into game-specific [Achievements] that's developer driven."
Nintendo's developers have expressed mixed feeling about adding achievements to their games, so this policy allows everyone to do what they want, as opposed to Microsoft, who requires that all games follow a strict policy regarding gamerscore.
Reggie also confirmed that Nintendo's much-maligned "friend-codes" will return with the Wii U, but Fils-Aime claims that the system isn't anything like what was used on the Wii.
"...you will be able to identify people as friends and have a certain level of interaction vs. a different level of interaction for the more general population. The method by which you identify someone as a friend is a lot simpler than what's happening today with Friend Codes."
For now we'll have to take his word for it. We'll know more when Nintendo explains more about the Wii U's systems.