Well, for starters this is my problem with 4e martial powers: the spamming of powers. One has specific powers that can spam (be it at will) or activate (be it encounter or daily) in exactly the same fashion in periodic intervals of his choice. In fact my problem is not that an encounter or daily stunt cannot be repeated at will but exactly the opposite: that one can freely decide when to spam specific powers or activate them. This is the core foundation of the 4e combat but to me it is totaly out of reality.
The only difference I see is that most "at-wills" don't rely on a lot of flash-bang to be useful. In fact, 90% of the time they have very little if no impact beyond a basic attack anyway.
For example, the four fighter at-wills are Tide of Iron (basic + 1 sq pushback), Sure Strike (+2 to hit, no bonus to damage), Cleave (basic + extra if you have an enemy near you) and Reaping Strike (bonus damage on a miss, otherwise its a basic).
With possibly Tide of Iron, I don't see any of those being particularly game-changing to use over and over. They represent strategies to attack (such as forms in fencing) moreso than actual maneuvers. One could almost envision the fighter saying "I'm having a hard time hitting him, should I improve my chances at a decisive blow (Sure Strike) or just go with a guaranteed small amount of damage (Reaping Strike)?"
Whereas most martial encounter powers DO represent those attacks foes usually fall for once (and only once). Striking two foes, guarding an allies retreat, knocking them prone, or slowing them represent the effects of specific maneuvers, and ones that foes rarely fall for again once they witness them in action. I think this is a better system than the spamming of combat options (famously in 3e, but I saw more than few called shots in 2e).
Dailies are a completely different kettle of worms. I've usually used the argument that dailies are techniques that are so difficult to master, they rarely come up in battle. They are also slightly taxing to use and require some element of "mindset" as well as proper training, luck, and timing (in short, being in the right mind at the right place at the right time). If most combat days are 4-5 encounters (personal estimate), that means they aren't necessarily rare, but not so common as the situations that encounter powers need to work.
I know such an explanation doesn't work for everyone. It allows me the ability to narrative justify it.