It doesn't matter what the semantical accuracy of the terms are - Damage Resistance, in the F:NV engine, means the damage taken is reduced by DamageResistance%. Damage Threshold means the damage taken is reduced by straight DamageThreshold (Minimum: Weapon Damage*0.2). If you have a problem with these definitions, take it up with the programmers of the game engine - don't argue that just because they're called that means they work in exactly the way you'd expect from a literal reading of the words.
(and yes, in FO1+2+Tactics Damage Threshold reduced damage by the DT amount - it wasn't an actual 'threshold' where anything over that acted at 100% efficiency)
So just because I call you Cheese Guy, you are now Cheese Guy? It doesn't matter what your name is, because I'm using Cheese Guy instead, and that is your name, because I said so.
Threshold is defined as - "the starting point for a new state or experience" - IE, the starting point at which damage can be taken.
Call it what it is. Damage Reduction.
Edit: Actions speak louder then words. The deed is done, and so am I.
http://www.newvegasnexus.com/downloads/file.php?id=35218