CPU and GPU processes are very different. Nvidia couldn't just go to Intel and ask to use their process. Also... there's no way Intel would let ANYONE use its fabs, they spend a fortune to ensure their process is first and fastest.
And LOTS of video cards come out with disabled cores. HD 5850, GTX 260, 8800GT, X800GTO, there's a bunch of others. What matters is performance, price, and then heat, noise, and power. Whether or not a card has disabled cores doesn't make any different.