This article says basically nothing. They only release Mario Kart and Smash Bros around once a generation because development times are too long to manage otherwise. New Pokemon gets released often because it's basically all Game Freak works on, so it's either be making Pokemon, or make something else. Even with Tembo, they only allocated a small team to make it.
Why does the article make it sound like Nintendo has been doing DLC for two decades? They say what they're doing with Mario Kart 8 is a standard, yet, it's completely new to this generation. Continued content for a game is not the reason they only do one release a generation, considering they've been doing this stuff since the SNES and N64.
All in all, this article smells like BS at best. I guarantee, Nintendo would turn out annual releases for everything if they could just because people would keep buying them anyways.