There is little doubt that the old bodies are getting long in the tooth, and many have been waiting for a replacement.
People have been taught that more MP is better, and it is ingrained into their thinking, in spite of the many experts who warn of such thinking.
When someone sees my camera, the first thing they ask is "how many megapixels" If a high MP body is in demand, buyers will get what they want because the company that provides it will get the sales.
I think the D800 is great for some users, and not so much for others. I hope those who buy the D800 are not just buying high mp by reflex and regret it later. I'd not be afraid to buy one except, I want better low light capability.
It is good to have a choice!