gonchuki
It does pack extra features however, TrueAudio, the new UVD decoder and increased tesselation capabilities certainly have to take some die space too. And there might be many minor internal architectural differences, like larger caches and whatnot that also need some die space.
While true, the bus width would still likely take up far more space than all of that.
Not only that, but AMD has already got the R9 290/290X bus down to a (comparatively) much smaller size, and that's 512-bit.
They're definitely up to something here, those numbers just don't add up to anything near what I would expect given the maturity of the process. Don't be shocked to see this is actually a 512-bit chip.