I was thinking weapon damage effects in group 2 were the elemental damages (nothing I can think of in-game requires a particular element to beat damage reduction) and possibly things like bleed, screaming, etc
While he specifically called out good and evil in group 3 Weapon DR effects... nonetheless those particular effects in NEW random generated loot as we speak FAIL to apply their DR quality to the weapons upon which they are generated. Thus do not in fact break damage reduction as should be intended.