Michael, you seem to be suggesting that the $4K USD price premium of the D3X over the D3 is due to sensor costs. While I have no information to the contrary, I doubt the D3X sensor is much more expensive than the D3 sensor. Yes, it has some Nikon goodies added to it, but it is still essentially an A900 sensor, and the A900 sells for what, around $3K USD. That's a body and a sensor for only $3K USD. I somehow doubt Nikon's added goodies drive the cost of that same sensor up by $5K USD.
I suspect - and again I have no information to confirm this - that it's purely market positioning driving the costs, not the components inside. Why would Nikon do this? Who knows. Greed is too simplistic an answer. Maybe they never intended to sell many, and just wanted to have the biggest, baddest, and most expensive DSLR on the market for bragging rights. Well, they succeeded, but at the cost of lots of bad feelings and acrimony from the Nikon faithful.
As a long time Nikon user, I was looking forward to a higher MP offering. But not at that price. Could I afford it - yes. But would I pay that kind of money - no. As an enthusiastic amateur, there's really no way I could justify it, and besides, I find myself being offended by Nikon's pricing policy, and I refuse to submit to it. I plan on laughing my head off when the D700X becomes available at a considerably reduced price (at least I hope I will be :-)
All that said, thanks for posting your views. As always, an informative read.