I believe John is correct. I noticed it when I got my D3. But I can't say it bothers me much because I think if you have the RGB histogram available you are much better off using that. Using the simple histogram, you can easily miss the fact that a particular channel is blown out. I used to have that problem with sunset shots -- blown red channel -- until I realized what was going on. On the D70, with no RGB histogram, all I could do was guesstimate how much less exposure to use. On the D2X and D3 (and D700), the RGB histogram gives a much more accurate measure. In the case of the D3 and D700, the larger LCD makes the RGB histogram easier to read than on the D2X, too.
I would urge anyone who has the RGB histogram available on their camera to use it and just ignore the simple histogram.
On the D3 (and, I assume, D700) the RGB histogram display also integrates the highlights indicator. I generally toggle back and forth between that display and the full-screen image. I have the full-screen highlights indicator display turned off. In all, I have only three displays enabled: the basic ones that you can't turn off (the full-screen image and the basic shooting info) and the RGB histogram. I find those three give me everything I need for normal shooting, and it's a pleasure not to have to step through a battery of displays to find the one I want.