Forget about inflation, exchange rates, and all that. Those are all excuses. The 5D3 doesn't have to compete with a 5D2 released at $2700 4 years ago. It has to compete with the D800, which has a much better sensor and sells for $3000.
Back to this again...the d800 has a great sensor for studio work and landscapes... the mk3 has a great sensor for wedding, events and sports. Can the mk3 do work in the studio? You betcha. Can the mk3 shoot landscapes? You betcha, can the D800 shoot sports, events, weddings...for sure it can. But is that where it is strongest? No for both. The mk3 is competing with the mk3 in a certain sense, but not really in the overall - each body specializes in one area of photography.
I have many friends here i nthe wedding business, both nikon and canon shooters --- and by and large whenever a nikon user asks other nikon users what they would choose if they wanted to upgrade to FF for weddings, they get told - d700, d3, d3s, or d4 if the budget is big enough. Even the ones that have a d800 admit that at a wedding it doesn't come out of the bag. Many mention the d700 cause its good in low light and has reasonable file sizes. These aren't my words, they are the words of nikon users!!!!
I agree with you that the mk3 is not competing in price with the mk2, that would be silly because the mk3 is much improved over the mk2.
And finally, at least looking at the amazon top seller list, the mk3 is currently at 13th on the list, with the d600 at the 12th spot and the d800 at the 16th spot ---and oddly enough the mk2 at the 10th spot. If this is similar to whats happening at the other dealers then the mk3 is handling itself quite well...