Well, schematics maybe, but an installed base is not total sales of a console, it's active consoles. That's what the term means, "installed in homes". That's why most believe the PS3 passed the 360 a few years ago in terms of installed base, because of the 360's higher failure rate. I see gaming news sites get this wrong all the time, which has furthered the misconception.
Regardless, about the Wii, I know the percentage of people who don't move on to the next generation is going to be high, I just hope it isn't nearly as high as the OP believes. The Wii U looks like it's going to shed a lot of customers, yes, but maybe a chunk of Wii customers have BECOME gamers because of the Wii and will try one of the other platforms or the 3DS.
Still, yes, the Wii was an aberration and I don't think its entire customers base should be included when we consider the home console market. Some of them just aren't going to stick around and never were. The 'shrink' is going to be somewhat misleading and doomsayers will try to use that as a huge negative.
There is still a lot of money to be made from the home console market.
