Anything over +1 never drops due to the structure of teh loot tables. The items are added based on the GP value of the chest, not a straight random chance, so a normal +2 weapon with no minuses becomes so high value in contrast you would never see it, and beyond that there isn't a chance it would drop, ever.
That's the reason shiny chain boots are rare, even with the penalties, and +2 monk boots with no penalties are non-existant.