If I get a forward observer created by the game let's say, he has attack 4 and def 8 - by removing his armor it then becomes impossible to find the armor the game offered me in the first place because the padded cuirass, for example offers 2 points of defense, but the padded cuirass he came with had 3! (You can see that from the drop down menu when leaving the cursor on his defense in the customizing/upgrade window)

That is true for all units offered by the game, their armor value probably refers to a previous version of the game and has not been updated. All units offered by the game are better than the ones I can customize with what is supposed to be the same kind of armors/weapons.