dont gpus have alot of things onchip for graphics specific stuff such as pixel and vertex shading (as well as others)... i think they even have different instruction sets to better handle graphics related operations...
Yes, the R580 from ATI has 48
shader units! My dual-core Athlon has..uhhh....zero. It has a 512-bit interface between itself and 512MB of DDR3 memory running at 1550MHz. My computer has a 128-bit interface to DDR memory running at 400MHz.
There are monster differences between how the chips work and the hardware they having backing them up. If only ATI had better drivers I'd have one of those cards *drool*... Ahh well the G71 should be released pretty soon and I'm reading a article saying Nvidia is going to lower the prices on their higher-end cards with this release. Fingers crossed it's not rubbish.