nvidia has much stronger marketing than AMD and takes advantage of it heavily. Most people, especially novices/uninformed folks fall prey to this all the time. Most of the parroted market speak seen in forums is a great example of it. On top of that, they have viral marketing, focus groups, and shills that invade many forums to further market their products. Plenty of companies rely heavily on marketing and marketing an image, look at Apple as a great example, I just always find it interesting how easily people are manipulated.
Also, there's plenty of driver problems on both teams, anyone who has owned products from both companies knows this. However, nvidia's drivers, which have literally destroyed cards from overheating and still have game-breaking bugs are amazingly still viewed as "better." For a current example, my friend can't play GW2 on his GTX 680 without reducing some settings because performance is awful; notice how that never got covered in any of the articles on TechReport, but stuttering on AMD's side did? For your reading pleasure:
http://lmgtfy.com/?q=gtx+680+gw2
Finally, consider the release of Titan. It's going to be faster than the GTX 680 and priced disproportionately so, but I guarantee it will be hailed as the second coming of awesome gaming cards. The 7970 did the same thing against the 6970 with a much better price/performance ratio, but it was lauded by critics despite better improvements. Furthermore on day one it surpassed even overclocked 6970 CF performance but again, no one noticed. I even made a thread about it:
http://forums.anandtech.com/showthread.php?t=2215295
I don't know if it speaks more about the rising ignorance of the enthusiast community, the poor coverage/review/ignorance of the tech sites they read, or something else. I can't complain because it is ignorance that allows things like bitcoin mining to remain so profitable, but I find it odd that some people don't pick up on these things.