But history has shown the statement not to be true. When 35mm sensors hit about 20MP, it did not seem to stop sales of the MFD backs/camera in that range. Nor did the companies seem really to suffer and you can still buy 22MP backs from Phase and Leaf and the sales are doing fine from what I hear. DSLR customers are not simply MFD customers with not enough money. In the silver age of photography, 35mm was not king because larger formats were simply more expensive. The DSLR/35mm customer is just a different animal. Just as the MFD/large format shooter was a different animal. Your mistake comes from thinking the choice is simply economic and based on matching the number of pixels. Art is not an economic problem.
They did not stop, but we did see a lot of work that was been done with medium format going to DSLR.
Since this is electronics; is not enough to have the same level of sales. Development cots rise.
There is a level of sales you really need in order to remain competitive.
For professionals MF system is an inversion that needs to be recovered. For wealthy amateurs it's not. So they do have the alternative of changing the market segment. Even if they do, so they need to invest.
1. The D800, even in accordance with DxO is still a DSLR in terms of color rendition. They can not touch the quality MF gives for still life. Hasselbad has the 200MS and Phase one the IQ180. I am on the theory that even the 40s will be better than the D800 on this application.
2. Remember that the IQ series has such a good result because of the low resolution mode. For the IQ180 it means 20MP more than needed on most cases, but less than the new Canon and Nikon machines
3. MF is not dead, not even close, but they need to act fast, before is too late and get push to a "looks" niche.
4. Remember that is a system component. The Canon and Nikon systems are far ahead. This includes increasingly popular the wireless and video options.