Traditional spells, prior to 4th edition's power system, in D&D varied wildly in power scale even at the same spell level. Every vancian spell is a daily power though maybe you can memorize it more than once. On top of obvious power differentials between daily powers and the rest, 4e also added magic item daily powers.
Short adventuring days were surely a potential problem in previous editions. Some classes could go all day while others wanted to rest as soon as they had used up their "most" fun abilities. Take the worst case: the wizard was useless as he followed along with his martial buddies after he cast only a single magic missile spell. Certain Dungeons Masters may have gotten used to the idea that one colossal combat per day was the right way to run the game.
Hopefully 5th edition will be able to simultaneously handle both ends of the spectrum through inherent design or clearly delineated optional rules. Perhaps Rodney says it best:
[W]e should be putting the tools in the hands of the DM to create adventures that contain only a single, huge combat encounter to cover the entire day’s worth of adventuring and still provide a satisfying adventure experience.Because, for some people, that's how they roll!