JimmyBean, synthetic 3DMark benchmarks do not translate over to actual games. While an OC'ed FX-4100 can score a higher benchmark than a stock i5-2500k, actual results from games show that the OC'ed FX-4100 yields lower performance.
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kai-fei, AMD prices their CPUs in accordance to it's performance level. For example, some time last we I responded to a thread regarding the a somewhat similar question you had with regards to a FX-6100. I used actual benchmarks from the following review and use the Core i5-2500k as a baseline. Synthetic benchmarks were not taken into account since they really do not serve any purpose when actual benchmarks are available.
http://www.xbitlabs.com/articles/cpu/display/amd-fx-8120-6100-4100.html
I calculated the performance difference for each game and application. I am not going to do that again since it was very time consuming, but overall the FX-6100's performance was around 63% for game and 64% for applications compared to the Core i5-2500k. Based Newegg's prices the FX-6100 sells for $150 and the Core i5-2500k sell for $220. That means the FX-6100 sells for roughly 68% of the price of the Core i5-2500k which closely correlates to the FX-6100's performance.
There's a thing called "Brand Loyalty" and that is the case when it come to people who will only buy AMD CPUs, but it applies to other things as well. For example, I only buy Levis "black" jeans. I did buy 2 pairs of Lee "black" jeans though since they were on sale and less than half the price of Levis jeans.
AMD's problem is that they over hyped the performance of the Bulldozer CPUs. It wasn't helped by a "fanboy" article back in January or February 2011 claiming that based on the Bulldozer design, best Bulldozer CPU would likely beat the Core i5-2500k by as much as 50% in overall performance. In actuality, Bulldozer turned out to be at best a very minor upgrade to the Phenom II. In multi-threaded applications the FX CPUs did show an improvement, but they are limited to people who do a lot video encoding, 3D rendering or WinRar file compression.
Power consumption is an other issue, though most people overlook it. AMD FX CPUs uses more power than Intel Sanfy Bridge Core i CPUs across the board. AMD's slowest FX-4100 CPU use more electricity than Intel's Core i5-2500k while idling and under 100% load.