Wasnt it confirmed that above equation doesnt apply to nostalrius simply due to them using a different but also possibly blizzlike formula, I recall people mentionning tests in beta and current patch.
Vanillawiki seems infiltrated with info up to wrath, I found the extract you are referring to, however I also found another thread here that lists dmg reduction as 35% with 310 wpn skill dealing 'almost' 100% of the damage again which would support the said nost formula.