Praetors and consuls maintained the necessary imperium to command armies. As such praetorian or consular imperium was necessary to command an army in the provinces, where administration necessarily in the Republic entailed military command (the imperium maius made this a more complicated question under the Principate). Quaestors and aediles, by comparison, were not the same kind of magistrates. The aediles were distinctly urban, and their duties did not extend past the city--to have provincial aediles would not have made a lot of sense. Quaestors could generally be found in the provinces on the staff of magistrates and promagistrates that outranked them. Hence the steady increase in the number of quaestors over time, as more individuals were needed to fill the administrative spots of the provinces, beginning with Sicily and Sardinia. In point of fact, proquaestors did exist, either because there were not enough quaestors to fill up the necessary spots in the provinces or because somebody's quaestor left his office for some reason. Verres, for example, whom Cicero so magnificently prosecuted, was a legate acting pro quaestore in Sicily.