MF lenses depth of field zone indication?

I wonder if theres some substitude for this very useful feature the manual focus lenses have, where you can widen your depth of field by focusing using the on-lens guide of focused area range depending on the aperture used

Shouldnt digitals (D70 here) have at least a program/function maybe doing that ? (push focus forth and back of the main focus area using the focus range each aperture provides, focusing not exactly where the main focus area is but somewhere before or after that acordingly, just keeping the main focus area within the given aperture focus range and gain more depth of field)

Or is this implemented already and used as default way of focusing in AF cameras?