Why do the iron, steel and silver arrows in my inventory all the the same (4) damage? It's only dwarven arrows that have more (5) - I have no arrows above dwarven. My character is a level 11 dark elf (Dunmer).

Don′t really know tbh. But you have to take the bow′s damage into account too

The damage value you see is not the base damage of the weapon, it's the damage modified by your weapon skill. At lower skill levels the differences aren't big enough for Oblivion to display and so will seem the same.