It's true that clock speeds aren't a reliable indicate of actual performance when comparing different chips - however, it's still true that newer graphics cards are significantly faster. Did you check out those benchmarks I linked? I know from my own experience that my NVIDIA 8600 is way faster than my Intel GMA 950, or my older Radeon 9800.As far as computing power. That is pretty much nothing. Checking the specs on my cell phone. It has a clock of 1900 mhz. So basically your buying the equivalent of 1/3 of a cell phone.
Where is the evidence to support your claim?
And many of those improvements are also there to improve performance further (e.g., shaders allow better performance as things can be processed on the graphics card without sending the information each frame).As I said.. the difference is better support for shaders, graphic technology, physics, and other aspects.
And try http://www.nvidia.com/page/geforce_8800.html for info on the shader clock speed. New Egg isn't exactly the definitive source of information on the technical details of graphics chips.