The core of your argument hinges on that the overwhelming majority of the market bases their purchase decision on graphical prowess, (and will thus reject the WiiU and rather sit around waiting for the PS4/720).
No, my argument is that the core gamers who buy a console each generation buy a new console typically because it offers their favourite core experience vastly improved (all tech, not just graphics) from the console they currently own. These console buyers bought PS360 this gen, and Wii U isn't offering them an advance on their core game tech so won't be bought by them. Thus it's possible Wii U, trying to sell on the merits of its touchscreen, controller will fail to sell to both this core and the Wii upgraders who aren't as enamoured with the pad as they were the Wiimote, whereas PS4 and XB3 will sell to their core audience. Hence, your reference to Wuu performance as indicative of all next-gen is faulted.
The number of PS3s and 360s sold to date is just under 140 million. I've seen rough estimates that half or so of these system are in actual use, any use. Accurate statistics are obviously hard to come by.
How many Wii's are in use? What has that got to do with upgraders anyway? Could be they aren't being used because the core that played them are wanting better graphics.
It seems you are arguing that a Wii user who bought Mario Kart is going to reject the WiiU because it doesn't represent a sufficiently large graphical step up from the PS360, but will instead choose to buy the PS4 and run GT6 on it? That kind of reasoning makes no sense at all.
Then you misunderstand my position. I'm sure there are Wii gamers who want better graphics, but Wii U changes what they bought about the Wii in the first place. Every Wii owner might buy Wii U to play Mario in HD, but it's also a possibility that everyone who bought a Wii play Wii Sports won't see the appeal in the Wuublet. Whatever the Wii owners choices, they won't tell us what the core HD gamer's buying habits will be.
The success of the Wii as well as the success of the 3DS demonstrates that it just isn't the case.
Wii and PS360 are different markets with different tastes. The COD and FIFA players of this world chose to go with the conventional HD graphics over Wii.
...and that's why I propose that if the WiiU fails, then it says something dire about the future of the console market as a whole, because there is no way that better graphics will bring in the masses to the PS4/720 if it failed to bring them from the Wii to PS360.
Better tech was enough to get 80ish million to upgrade from NES to SNES, from SNES to PS1, from PS1 to PS2 and from PS2 to PS3 (or alternatives). Wii operated in parallel, not an upgrade path for these tens of millions of users, but an alternative experience for new gamers as it were (with some crossover of course). Wii U offering a graphical upgrade to Wii owners may fail because Wii owners didn't buy on graphics but interface, and Wii U is principally offering a very different interface. The Wii customer may or may not be interested in Mario Kart HD. But the COD and FIFA and Halo etc. players are going to want to play their core AAA games in HD with better graphics just like every other generation. You need to present a case as to why these cores gamers won't want another round of tech updates.
Remember console sales this gen are over 220 million. Let's say half of them are the core gamers wanting better tech upgraded every generation, and half were only interested in novel experiences. That's 110 million console owners not being served by Wii U who will be served by PS4/XB3. In what way is Wii U thus indicative of the XB3/PS4 market when it's dealing with different consumers?
And whatever reductions you want to make in those numbers due to failed hardware or unused hardware, you have to also apply to Wii. It's not like this gen is 90 million active Wiis and 60 million combined PS360s because they all break or people are bored with them (unless you can present evidence of that).