because the R700 series is fairly old.
All joking aside, the R700(HD4xxx) is from 2008, but it is also the base for the R800(HD5xxx) and the newer R900 (HD6xxx) series....
(I think).
So if Nintendo started with a base of R700 and customized it with features from the HD5xxx line like Eyefinity and DX11 compliant shaders/effects and maybe some other stuff from the the HD6xxx, then they wouldn't have an old GPU at all. They would have a fully customized monster that is as modern and new as they want it to be, but with only the features they want/need.
I think one of the three console makers are going to bow out next gen. My money is on Sony. Where will the haters go then?
I don't think this next gen, but maybe the one after. But if someone where to sit this next one out and wait for the one after, I would guess that would be Sony. MS is already elbow deep in it's next gen machine and the chips are supposed to be ready sometime early-mid next year....
if the rumors and comments of an AMD Fusion chip are to be believed.