I think Nintendo were quite smart this gen by avoiding a head-on three ways and carving their own market. While there is crossover of course, it's clear that the PS2 upgraders' market was stolen by the 360, with that huge pool being split fairly evenly across the PS3 and 360.
Aside from the usual massive market of Nintendo's core audience, Wii was popular with folks who wouldn't normally game at all and would only play one or two titles, such as Wii Fit or Just Dance, which is a huge market. This is the market that Kinect is gunning for with some success, as Nintendo seems to have largely abandoned the Wii while the WiiU seems to be a cross-over back to the PS3/360 core. Perhaps they sense Sony is in a weak position moving into the next gen, so Nintendo is going for blood.







