[Shodo]

Your dps is based off of strength as well - if he had a lot more strength than you he would be hitting for more damage more often. If he was wearing a haste item and you were not, that would affect it as well. Or if a shaman/ench in the group was giving him a haste buff, but not you (a lot of times they'll only haste the "dps" classes to save mana).

Not sure if different classes have different formulas for calculating attack rating, but that might affect it as well.