This might be a bit revisionist, and it also completely ignores the differences in the industry. GPUs and other tech benefits from (mostly) regular improvements that greatly increase the efficiency of said products. This improvement does not come for free of course, but given the healthy margins the leading companies in silicon are running with, it's very obvious that the increase in cost currently out-accelerates the cost of the the products themselves.
There's no such driver for headphones. Improvements are very infrequent, and only occur after a great deal of investment. The market (especially at the high end) is extremely small vs. the GPU / CPU sector as well. It's also very important to note that the margin you speak of does not really exist with the manufacturer, but with the dealers. For instance, many higher end Sennheiser headphones are sold at 3-4x what the dealer purchases them for. Your reference would work better if NVIDIA were selling these Titan XPs for $500 and the retailers were selling them for $1,500. I'm told this is not even remotely the case.
Lastly, "flagship" headphones have existed in the multi-thousand dollar category for decades, including electrostatics from STAX and AKG. The HD800 most certainly was not the headphone that opened that market up. It did however exploit a market between the $500 and $1,000 categories.