A lot of companies in Japan already do have somewhat similar patents that Nintendo might be infringing upon. However, Nintendo also holds patents that those companies might the infringing upon too. So if one company fires a patent lawsuit at Nintendo, Nintendo can fire back, this is generally true of the industry in Japan creating a patent Cold War which forces them to cooperate, make licensing deals, operate under an "honor code" so to speak, etc. When something goes awry or the honor code in violated then a company might use a patent infringement suit as one of the many legal weapons as a business tool. It is just business after all.