The thing is these games do sell at those prices. Look at the most recent example, New Super Mario Bros. U. At least half of all Wii U owners if not more own it. While it may seem unreasonable to a lot of people who aren't big fans of the genre, it's very reasonable for fans of the genre for the simple fact that we really don't see a lot of investments in high quality 2D or even 3D platformers anymore. Older core gamers buy those games because they miss those types of games. They're ideal for little kids because the learning curve is simple.
Also, someone on another site tried saying Nintendo has been flooding the market with these types of games, which simply isn't true. It all goes back to the fact that there aren't too many of them anymore. That means every time Nintendo releases and markets one of those games, it gets a lot of attention from the press.
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