Among the gaming fanbase there are two groups, people like myself who spent months following a game up until launch, knowing most details and keeping a release in the forefront of our minds fit into one group. While, alternatively, there is a second group who are big game fans themselves but they don't research, this group sees an advertisement on TV and takes interest, or just casually strolls into a game store and takes interest. It is the latter group that is the tougher market and can make up more of a games sales and in the case of Splatoon is likely where the sales have been found.
Nintendo is not known for advertising their games, it just rarely ever happens. However, Splatoon had quite a strong marketing campaign behind it which was hard to miss. It seems funny, Nintendo recently reported that Splatoon had sold over one million copies but the company is actually surprised by this and the games success. Nintendo discussed this during their recent shareholders meeting where Satoru Iwata actually pointed out advertising as part of his statement:
As some of you may have seen the TV commercials we have been airing recently, “Splatoon” is a brand-new title and not a title from an established series. It has a very unique and fantasy-like setting. This game, inspired by squid squirting out ink, is played by human-shaped characters with squid-like features shooting, instead of squirting, ink at each other, and the team that paints the widest area in its team color wins. Having received high recognition from our consumers for its novelty, this title’s sell-through sales reached 1 million units in less than a month from its release. We feel very grateful for this, since our view was not so optimistic prior to release, for it being a non-series title.
Hopefully Nintendo will learn in the future and will do better with their games because clearly it helps to drive sales, even on lesser platforms. Alternitively, this could even cause Nintendo to take more game risks in the future but we will have to wait and see.