The business reason is this. Nikon is splitting their customers into the following:
(ignoring the P&S audience for this discussion)
Pros - use FX camera and lenses.
Amatuer - use DX camera and lenses, unable to upgrade body without upgrading lenses
Film - using film camera, and FX lenses
Since FX has been in existence for quite a long time and DX is relatively new, they are hindering their amatuer line. What do Amateur people tend to want? They want a regular lense, they want a zoom lense, and they want a wide angle lense. Its also worth noting that Nikon had "DX" sensor before they had DX lenses. When the d2h was being sold, it was obviously a DX sensor, but you could only buy FX lenses. So I (and others) had a camera that wasnt able to support their lenses... you made due. Obviously you purchased FX lenses. then they came out with DX lenses. You thought, "hmmm... i guess i should buy it, its more appropriate for the camera"... now you have both DX and FX lenses. Then Nikon releases the first full frame, and amatuers think "wow.. cool, but beyond my price range". Same for the d700, and probably the d800, when it comes out. For people who are doing this as a hobby, and not a profession, its hard to justify that sort of money. But at the same time, they are pigeon holing their market.
Where does the company make the most profit? Well, their P&S, obviously, but after that, their bodies. We know the statement: "glass lasts forever, cameras do not". From a pure business sense, it makes sense to create an FX camera that has lower specifications than the d700. You want everyone to be using the same lenses, so they only have to produce one type, and so its easier to upgrade bodies (again, because Nikon makes more profit from upgrades). right now, Nikon is missing a lot of people who might upgrade their bodies because to do so they also have to buy a whole new set of lenses. Its just bad business. You can make the counter-argument that if someone wants a great FX lense, they have to buy the great FX camera too, thus increasing profit, but I would postulate that Nikon loses more than they gain by keeping hobbyists out of the FX market.
It made sense at one point in time. I dont believe it does anymore.
also, your point about the d700 goes to further my point. Yes, they will be out there at some point, and cheaper, but Nikon gets none of the used camera money.
I completely get that pros NEED to have better cameras than me, a hobbyist. I also think that Nikon is really dropping the ball on this one.