It's only after releasing the 9800gtx+ (an overclocked 9800gtx)
256bit
GeForce 9800 GTX+
that enthusiast were able to acknowledge, though not wholly, that the new card was now the new king of the hill.
That card, same with the gts250, was able to address buswidth-bottlenecking through faster clocks and not capacity.
Nvidia was not slow to notice this also. The next generation cards, the Geforce 200 family, sported wide bus widths which they were most notable of (gtx 285/275).
But these cards were power-sucking furnaces so with the next generation (gf100), Nvidia favored memory clock over bus width but maintained memory capacity. (But this is out of line already )
^^ clearly, its not just bit after all.
bus width is an all important highway, but what matters most is what passes through it, a bike? a trike? a pison? a school bus? a ferrari?