Why would you worry if the encounter is balanced, is every single encounter in the world self-adjusting to the level of the PC's? Shouldn't the power level of what the PC's encounter be based more on what should be there? A squad of warriors going to join a crusade could be all fighter types and not a balanced party, and probably low level but seriously outnumbering the PCs. A famous wizard and his entourage may have a single very high level wizard, maybe a few lower level but still decently skilled apprentices, some low-level hireling flunkies/servants with marginal combat skill, and maybe a single cleric to tend to the wizard as a confessor/personal physician. If the PC's run across a party much larger or more skilled (higher level) than them, they probably should look more into hiding, negotiating, bribing, not antagonizing the other party, and not engaging them in combat.
Also, while I'm not exactly up on 4e design, why is it bad to use PHB PC rules for NPC adventurers because of daily powers? Prior editions of D&D had NPCs with daily powers, it was called spell slots, and most DMs I know assume that typically NPC spellcasters have a full loadout of powers unless they explicitly have a reason to be low (like had just left a battle before encountering the PCs).