Maybe I am totally missing something, but it seems to me that the Avenger's ranged powers blow. They just do so much less damage than the melee powers -- any time I see a 2d10 ranged power, there's a 2[W] or 3[W] power of the same level available, and [W] can easily be at least a d10 if not d12 or 2d6. Sure, the ranged powers have some neat effects, but the melee powers do also, PLUS the melee powers get the Oath reroll. It's so bad I've tried building an Avenger/Cleric just so that I would have something to do with my implement other than abjure undead. (See cascade of light, a cleric daily 1, for an example of a leader power that out-damages the striker's powers.)
So, I think adding the Oath reroll to the ranged powers would be completely balanced. You might phrase it like this: "When you make a ranged attack against the target, and making the ranged attack does not provoke any opportunity attacks, you make two attack rolls and use either result. Your ranged attacks do not provoke opportunity attacks from the target." I would make this an alternative to the regular Oath power -- you have to pick ranged or melee. If you pick ranged, then you get proficiency in military ranged weapons instead of military melee weapons. I'd maybe replace Censure of Pursuit with Censure of Discernment: You get the damage bonus against an oath target who moves behind cover or concealment, or moves farther than 10 squares away from you. Or something like that.
-- 77IM