The fact is that for most studio usage, the 5DII and A900 will do just as well as the D3x, but save the photographer enough money to buy a new high end Mac Pro workstation and screen.
That seems to point to the the sad fate of cameras like the D3x and also the 1DsMkIII: most of those who need more resolution than the D3 or 1DMkIII provide mostly do not have a great need for more than the 5DMkII and A900 offer. And I suspect that even dropping the wholesale price difference to match the manufacturer's cost difference would not help greatly, so Canon and Nikon are now stuck with high markup, very low volume "prestige" items at the top of their product lines.
As evidence, Thom Hogan reports that despite greatly reduced demand for the 1DsMkIII (due to the 5DMkII in particular I suppose), Canon has not dropped its price to dealers; retailers have just been forced to accept far lower margins along with greatly reduced sales volume.
For now the D3X at least has a few Unique Selling Points over the 5DMkII and A900, but the list is rather thin:
1. access to the Nikon lens and flash system and professional support, particularly compared to Sony's A900.
2. 100% VF coverage vs less for the 5DMkII
3. 5fps vs 4fps for the 5DMkII
4. better AF system (but how much does it matter for careful, deliberate high res. work?)
5. Integrated vertical grip (is that overall an advantage or a disadvantage for non-action photography?)
I suspect that after Nikon has cashed in on item 1. in particular, it will have to put a D3x-like sensor in a D700-like body, to grab a share of the far bigger sales that the 5DMkII and A900 are getting. And that cancels items 1, probably item 4 and maybe item 5. So how much will a 100% VF and the unremovable extra weight and bulk of a non-removable vertical grip all to the value of the D3x then? And a 100% coverage VF is surely doable too in a $3,000 DSLR, as the A900 already shows. (Even the far less expensive E-1 and E-3 have that much.)
My optimistic interpretation is that except for high speed action photography tools like the D3 and the 1D series plus a very small "prestige" market, very good DSLRs in full 35mm format will soon have little or no reason to cost more than about $3,000. At least for the landscape photographers that we allegedly are around here!