Nintendo has been around for SOME time. They've gained a lot of fans and haters alike. They duke it out here. Well, not really but the forums aren't restricted to sales. Numbers themselves are interesting, but they aren't that interesting to drive an entire site.
In addition to that, it just depends on the time. Sometimes you see the forums saturated with Sony, sometimes it's Nintendo, more not than often, Xbox may show up. With PS and XB being so similar, there aren't many differences to talk about besides OS software...which isn't that exciting. It matters about content and even though Wii U isn't a big success, they do have a lot of exclusives that get a lot of attention from their respective fans.
Overall, it's a lot of stuff. Just make some Sony threads or something yourself to balance it out. Anyone can post after all...unless you're banned that is. XD