Yeah, I find the whole daily power recharge more disconcerting, and far more balance-bending too. Two groups will go into an adventure, and one thinks that resting at any time other than "between adventures" should be avoided at all cost, while the other sees no reason not to rest the equivalent of every other room.
Critical issue here: the DM.
This is a problem only if you view the scenario in a vacuum. If each group of monsters is fixed, never returns from the dead, never moves, and is thus a predefined, unvarying obstacle the party must overcome precisely once - then indeed, whether the party rests a lot or a little is merely a choice that might make things easier or harder.
But if you assume the DM's interested in his story and somewhat competent, this works out entirely differently. There is probably an external world and taking weeks to clear the caves as opposed to a day may have consequences. The monsters (or different monsters) might come back if an area is left alone long enough. Or they might communicate and overwhelm the PC's if they're left alone long enough. Even without active cooperation, they'll likely notice somethings amiss, and individually prepare.
And the best part about these balance "workarounds"? They turn monster stat blocks into a living, breathing world in which the PC's can't just stomp one encounter after the other, they need to think about what it is they're doing, and who they're doing it to. Some challenges will best involve lots of resting; others fast action with little resting. Sometime you'd best avoid short rests (keep the enemy confused), and if you take a break you might as well take a few days. Other times short rests are fine, but long rests let the enemies fix the holes in their defenses (say, a more sparsely populated dungeon but one that's intelligently defended).
If the game introduces mechanics taking that choice away from the players - i.e. every encounter they're at almost full strength regardless of previous decisions - then you're taking the flex out of the system. Denying a short rest suddenly becomes akin to a death sentence. The PC's
need to approach each monstrous home invasion
similarly - they need to rest for a short while after every encounter; and they might as well try to go on as long as possible since they can't really control how long they can last in a day anyhow.
Encounter powers by themselves don't cause this problem, but for them to shine, they could use some tweaking. Say, a fatigue system of something, as you suggested
.
