I absolutely see the difference in the pictures but I would not be willing to say the image produced on the GTX480 was "better" than the one from the HD5870 (or vice-versa), it's just different. If you really look at it, I see all the exact same regions and forms in both, but the gamma does not look the same in the two pictures, and neither do the RGB values. The GTX480 picture looks to have slightly higher gamma and slightly more green, which makes some of the areas pop out more.

For the record the last two cards I have owned were an HD5850 and an 8800GT, so I could care less who I buy my cards from. This seems like an irrelevant comparison from one site.