Eh, one arose from the conquest of other countries (Germany), while in this case the Empire divided itself internally*. The Republic turning into the Empire was a coup supported by both the military and the core after all, not a series of quick military conquests on their neighbours. I don't think comparing the Moff system to other systems of government IRL is the right thing to do in this case. We all know what it is on face value: a series of military governors with sweeping powers subservient to an autocratic central authority.
I don't see much point in continuing this line of discussion, because it seems like a bit of a nitpick, I'll be honest!
*Of course during it's early years, the Empire conquered several unaffiliated territories, though those were quite small compared to the territory it already possessed, hence my statement up above being true in 95% of cases.