I personally haven't had any trouble with explaining narratively the powers for both martial and non-martial powers.
Blinding Barrage: It is exactly what it says it is, the Rogue in a burst of movement sends a barrage of projectiles into the eyes of those around him. The reason why it is only once per-day, is the chances of him pulling this off is so small to the point where the chances of pulling it off are once per day.
Yes, it is not necessarily gritty, realistic medieval warfare, but it isn't magical. *Shrugs shoulders* I don't see why backflips, martial arts-esque moves, etc. have to be considered not appropriate for "low-magic".
Divine Oracle: Well you can explain this in different ways. One the literal sense, where being a person who siphons off the power of a god, he can alter time briefly to allow a second chance.
Another, the more heightened sense of the future that the gods have allow you to tap into that in mid-strike, and realize your about to miss. Allowing yourself to quickly ready another action.
Another, the attack actually never happened in the first place, and there is no time-change or anything. Simply, you get another chance out-of-game and in-game that first time never happened.
Own the Battlefield: This power works if you believe that throughout the encounter the Warlord has been subtly working and playing with the enemies to get them into positions that he wishes.
In-game, I never ever imagine players and enemies simply standing there in their little 5 by 5 feet boxes, their running all over the place and attacking, etc. even inbetween their moves.
It is simply when a power is used, this is when it actually works or its significance comes into being. Which be the case in this instance, when Own the Battlefield happens it is when all those enemies in the burst have been positioned finally where the Warlord wants throughout the course of the fight.