I am thrilled about the D800, it has everything I will ever need from a camera. Except for the one thing I really was looking forward to: the ethernet/WT-5 connection the D4 has, with all the advanced possibilities of remote controle. What would be the reason Nikon chose not to include this in the D800 - because the RAW-files in this size would make wireless transmission too slow?
The WT-4A (which I have) reportedly will work with the D800. I use it with my D3 in my small studio to send images to my laptop for real-time client review. I never send the raw image as that takes too long. I shoot Raw + small jpeg and send the jepg only. That goes quickly. I suspect that even with the WT-5's higher data rate it would take a long time to transfer D800 Raw files.
An RJ-45 port is a pretty sizable port, not only W & H but it extends pretty deep. The connector takes up alot of internal space before you even deal with the electronics. The D800 is a smaller body than a D4.
Also, practically all prosumers know how to use USB and most likely already have USB ports on their computers they can plug the camera into. I can hazard a guess that not all prosumers know how to deal with RJ-45 ethernet connections, or even have an available free RJ-45 port on their ethernet switch/DSL router/etc. Unlike the casual use model of USB, devices that are connected via RJ-45 ethernet ports tend to be things you want to keep plugged in all the time, so you aren't going to be unplugging something to plug your D800 in.
Saying all that have they ever developed a "mini RJ-45" port that will take a dongle to convert it to a female RJ-45? That would be the ticket to reducing space use.