The threshold does two things
1) It says what enhancement bonus a weapon must have to make a difference at all.
2) It is also the reduction that applies to the bonus.
The remaining question is: Are the final numbers for the Greatsword "upgrade" to the Ogres correct or not?
They might be "self-correcting", if we assume that a Greatclub grants a +1 proficiency bonus, and a Greatsword grants a +2 profiency bonus, compensating the +1 magical threshold.
Considering that the equipment changes also change the armor from whatever they usually use to (nonmagical) Full Plate, and the article lists the total benefits as +3 to attack, damage and defense, I think it's reasonable to assume that the total benefits are the sum of magical and "mundane" modifiers from the new equipment. The AC improvement hails from the full plate, the attack bonus from a higher proficiency rating and a higher enhancement bonus. (and the damage bonus comes from the different weapon used, too. I presume Greatclubs deal less damage then Greatswords)
cferejohn said:
Fair enough. But the War Devil entry says nothing about the + of the Trident, so if the PCs take it from him, how do we know that its +5 or +3 or whatever?
You don't know it from the stat block, but you know it from the treasure you wanted to assign to that encounter, according to the presumable existing guidelines for treasure per encounter.
