Very interesting question! I've always been facinated with the history and mythology of ancient Egypt (Kemet), as my login name might indicate, but your question leaves me baffled! I never thought about it in such a way before... perhaps I need to go back and hit the books again!
From the hip: As I understand it, the Pharaoh was considered a direct decendent of the gods and thusly ruled the lands as, what we would call in D&D parlance, a high priest. So, the hierarchy of his/her "nobility" would be drawn from the priest class and have no proper title as respects to European nobility (i.e. Duke, Earl, Prince). Taking it a step further, it may be as well that these lesser clerics had no "fiefdoms" to lord over, for anywhere outside the Nile fertile zone was a pretty harsh existence.
This is all off-the-cuff conjecture, but you've stimulated my interest to investigate the idea some more! Take care!