Ubisoft can give an exact release date because they have moved to a yearly release model, with very defined periods for design, development, QA, and so on. Nintendo is still organised so that developers come up with ideas and see them through to creative completion, whenever that might be. Pikmin 3 and SSB were announced before they were even in full development, because Nintendo felt they needed to mention them. AC4's announcement was just one matter-of-fact milestone on the list of hundreds, coinciding with the ability to release a trailer and screenshots.
Iwata needs to get better hold of his development staff and treat it like a business, with games being released on schedule in support of the existing consoles, instead of game ideas targeting whatever and whoever happens to be available to handle it.