More choices doesn't necessarily mean more sales. Most of the growth in the exchangeable camera market comes within the mirrorless market. Only the Leica M is a true mirrorless, 35mm camera. The D3X and 5DII are available because Nikon and Canon haven't managed to sell the remaining stock. They are surely long out of production.
I know so many photographers with a 35mm DSLR sitting at their desk, and an OM-D or a NEX in the camera bag. As volume models, the 6D and the D600 make sense. All the rest will have to fight for market shares among a relatively small group of professionals and enthusiasts, and even many of those are going towards smaller formats.
These are and always have been expensive products. Consumer cameras, compacts, mirrorless, APS-C DSLRs, always sell at higher volumes. Growth usually is greater in new markets as old markets approach saturation (I am more likely to buy something new than replace what I have). But you have not actually shown that the FF frame market is diminishing--you can get growth in one sector and while another sector keeps the same sales but will simply look smaller--if one year I make $20 dollar selling FF and $80 dollars selling everything else and the next year I make $20 dollars with FF and $120 dollars with everything else does not actually mean I am losing a market even though the share of the total decreases.
Every cycle has a point where the new model coming out is timed while the old model is there (production usually ends long before stock runs out). The point I was trying to make is there are many FF models available. The interest in the 5D MkII, D800/E, Leica M, a99, and RX1 releases certain show a great deal of enthusiasm in camera enthusiasts, if GetDPI and a number of other forums are any indication. Certainly these people are buying these cameras. (For all the photographers dumping their FF for smaller formats, a surprising number of threads featuring new FF by GetDPI members seem to be coming up. Even Amin of Serious Compact fame bought a FF camera.) I don't see a demand problem.
As far as arguing that the cheaper models sell better than the more expensive models, when has that never been the case? Expensive cameras tend to have a smaller market, but expensive cameras are sold. I am sure Leica will sell their new S. But I am also sure more D600s will be sold.
