Whoever stated that the D700 cannibalized sales from Nikon is mistaken. Yes, perhaps if photographer had the money and didn't mind the extra weight, they might have bought a D3 or D3s. Or they might have skipped the purchase entirely and stayed with a DX or (perish the thought) gone to another brand.
Now consider all the accessories that the D700 owner bought. I bought a 28-30 2.8, a 16-35 f4, a 70-200 2.8 and a 200-400 f4. These were all bought after I decided to migrate to a D700.
I want high ISO, low noise, no extra workflow time in having to downsize files, faster fps, and they can throw in video. I'm not saying that the D800 is not fantastic but it is not a D700 replacement in my mind.