Nikon pulled the site with the Nikon D300s LCD screen image few hours after my post. Today all images from the histogram article were replaced with D5000 LCD screenshots.
It appears that the Nikon D300s will have a new histogram zoom feature (selects only certain area of the frame and displays the histogram) which is obvious from the rest of the Nikon D300s screenshots from the same site which I did not publish yesterday:
All leaked Nikon D300s LCD screenshots seems to be in 16:9 ratio. It is hard for me to believe that the actual LCD screen will be with a 16:9 ratio (maybe it can be set to display in 16:9 mode or the images are just cropped that way) – here is the current histogram from a D5000 from the same site for comparison: