With headphones, your listening in "2D" (left and right). as you only hearing whats coming from the right channel with right ear. and left channel can only be heard from left ear - Well that's it.
So if you like to say that headphones don't sound real at all - fine by me. but i much rather listening to headphones as there were meant to be then try to fake a realistic soundstage. the fake sound signature of the hd800's is fake enough..