This is absolutely absurd. There is an astronomically huge difference between sensors build-wise. as technology advances, ships get smaller and smaller and the cost to produce them shrinks as well. With cameras, this is not the case. Cameras are one of the few exceptions where the larger the chip (sensor) the better the product. The large sensor of a full frame camera is many times more difficult and more expensive to make. With a sensor, you cannot replace a part of it if there is a defect, and the larger the sensor, the greater the possibility do a defect. Due to this, many more full frame cameras are thrown out during the inspection phase than APC chips. So you are not only paying for your sensor, but also the ones they had to throw away to make that one.
Also, the larger the sensor, the more difficult it is for the camera to focus, expose, process the photos, and maintain high shutter rates. This means more advanced technology and higher prices.
That $2,800 D800E is made from technology that has been updated since the release of the D300 and D700. Technology that costs a lot more to make and very likely to have defects present. There is a reason why camera cost as much as they do and why certain cameras cost more than others. I mean I am sure you can understand the increased level of technology, expensive technology, required to process a 36mp FX image compared to a 12.1mp FX one from a D700 or even more so than the image from a 12.3mp DX D300.