Well, you could argue that High Crit states it only works when you crit with it (it being the weapon that has High Crit), so doesn't work when you crit with a power that doesn't have Weapon. Yeah, I know it becomes an Implement, but that just lets you add the Enhancement bonus to attack and damage rolls with power channeled through it, and let's the magic crit work on the power as well, but nothing else gets to tag along unless the magic item says so, like in the case of the Holy Avenger.