There are relatively rare random attributes for items (such as the suffix 'of angels') which increase their value to merchants, but do not give any other bonus. In this case I think it is a hidden attribute, rather than the 'of survival' suffix (though I'd have to load a save and search through my loot for another instance to make sure).
This bonus value works best when you find such items and sell them.
Found in the wastelands, worth 50,000 gold (I assume the 'silver' part is what bumped the price up);
Silver Long Dagger Of Mater Warriors
Durability 10
Damage 9-31
+4 Strength