If AMD is going to compete, they need to change their reputation, and that takes time. Their performance is fine right now, but they still have a bad reputation because of drivers. For most the life of the 7000 series, they have experience stuttering in single GPU setups, and still microstutter issues in multi-GPU, and until the end of 2012, they were slower.
If you are buying a single Radeon now, it makes since, but if you bought it a year ago, you would have had an inferior experience. If you go crossfire, you'd still have an inferior experience. I imagine most people have purchased a least a couple AMD/ATI cards in the past, and also Nvidia products and have noticed the difference. I know I have. But after you've experience both sides, most people tend to prefer Nvidia, and then just stay with them.
AMD has improved a lot, but they are still behind, and when they finally catch up, if they do, it will still take a few years before people give them a fair shot, due to their reputation in the past.