From the couple of years I've seen I'd agree there is always a lot of Nintendo discussion and its fans are probably the largest section of active users.
Why do you think that is here? Chance? Did excitement about numbers from the Wii draw them in to this site?
Wii was definitely the reason. PS3 was doing awful and the 360 was holding its own, while Wii was breaking records. With Twilight Princess as a launch title, there were quite a few out and about. The DS always did well and by the time the 3DS recovered, it made up for the early death of the Wii and the Wii U struggles.