Most folks do not use manual focus, so in the general case the inclusion of the manual focus aids would just clutter up the viewfinder, in theory.
I thought about getting a KatzEye screen for my D700, but I just don't do enough manual focus work to justify it. The downside to the KatzEye screen specifically for the D700 is that it is a split prism only, no macro prism ring around it. All the other models have both.
---------+---------+---------+---------+ Joseph K Seattle, WA, USA