Don't you mean 4-5x as much?
And yes, yes I do.
They are not directly comparable. AMD's performance/transistor, watt, and die area is currently much superior to Nvidia's. It's especially ridiculous when the full Fermi GF100 die has 3.2 Billion transistors at 529 mm^2, and runs the shaders twice the speed as the rest of the chip. Over on the AMD side of things we have Cypress XT with about 2.2 Billion transistors on a 334 mm^2, running a single clock domain over the entire chip that is running much slower than Nvidia's shaders need to be at.
While generally the GTX 480 is considered faster, not to mention 4x the tessellation capability, larger memory bus, and CUDA capability which adds to the transistor count most surely, Cypress holds a good position near it. With some pieces of software, it equals Fermi with 2/3 the transistors, much lower power consumption, and smaller die area which is good for heat output.
I would liken AMD's graphics as to like many Japanese cars. Highly efficient, well engineered for their intended purpose. Nvidia's graphics are more like an American car. Heavy, and large-muscled with a very high theoretical capability through sheer brute force, but at the cost of fuel and efficiency.