I think ExploderWizard hit the nail on the head. Sometimes, you just want to get by those guards, and you know they've only got three hitpoints, so you say, "I swing my axe mightily at his neck and try to behead the bugger before he makes any sound" and you know that you deal at least three hitpoints, so if you hit, his head is detaching from his body (of course, when you make declarative statements like that is when you roll a 2 and miss).
In my games of 2E and such, I actually give fighters an ability that I call "Feng Shui fighting heroism" (a shout out to the Feng Shui roleplaying game) - which basically says that fighter characters (and NPCs) can attempt great feats of heroic action which 1) make the fight more of a spectacle, and 2) create some cool beneficial result. The thing is, no such rule is needed, because they could always do that - but I just put that on their sheet because new players don't understand what they can and can't do, and get stuck in the "I swing, I miss, my turn's over" business. It gives them something they can point to - "I'm using my fighting heroism ability to fire arrows into the giant slug, creating a makeshift ladder for the other fighter to climb up."
I can't see any reason why you couldn't do the same thing in 4E. So your "at will" ability says it dazes the opponent, and the little flavor text says you do it by whacking them in the head. What's the difference if you reflect some bright light into his eyes with your shiny sword blade? No difference at all to the end effect, so why not let them do it? You shift - do you do it by slowly walking backwards, or by doing a backflip, or some par cour, or whatever? No difference to the result, but one sounds cooler than the other.