that chart is based on:

Well, after this brief review to improve NVIDIA and related improvements DirectX 11, you teach that supposedly characterize the graphs in the next benchmarking graphics from NVIDIA. L The data used are based on a review conducted by the ATI techreport.com 5970, and has been a 50% improvement in FPS on the GTX 295, NVIDIA reported as improvements in the environment of 40-60% compared this graph.
so GTX 480 numbers are based on supposedly NVIDIA claiming that it will be 40-60% faster than a GTX 295;
they never say these benchmarks were run with real hardware

It's fake, follow the link and a comment says the 480 is exactly 50% faster than the 295 in every test. Definitely not legit.
maybe you should read more attentively