After something over 100´000 clicks on D3, D3X and D4 "in the wild" for macro work, I think I can confirm that you have nothing to worry about. The only problem I have had (other than nose marks ... why can´t Nikon make a glass that is resisatnt to insect repellant and sun-block) has been a huge scratch right across the screen of the D3X.
Ah ha, you say!
This was cuased by me being unbelievably stupid and putting a diamond glass cutting knife in my camera bag with the camera.
Was it stupid? - yes. Would a cover have prevented it? - probably. Is it likely to happen again or in normal use? - no.
So unless you are lady with cut diamond rings on your fingers, it is probably nothing to be worried about. And seriously, if I wore a diamond engagement ring or anything similar I would definitely have covers on my screens.