Baldur's Gate : The Sword Coast Chronicles : NWN2 Persistent World

come to the underdark and we can test it.

It's 10/magical for PnP reasons only, pretty much. It's there to promote the mystical otherworldliness of the monk's psyche, in that should they encounter orc/goblin hordes, peasant uprisings or bandit raids, all of whom use unenchanted weaponry in PnP, a single (powerful) mendicant monk with 10/magical DR could hand them all a serious ass-whooping and come out the other side basically unscathed and marvelled at by the survivors/surrounding communities and then preach their monk dogma and get some converts.

On BG the DR aspect of the feat is nigh useless since even CR 5 goblins tote +1 weapons.

hence why most /magic were changed to /addy

very few mobs use addy weapons

That would be good, if it were of value in the world in which these monks are existing. i.e. BGTSCC.
So yes, if it's not addy, +3 etc. Then ...

As someone who has a character with nontrivial levels in monk, I can verify that yes, the 10/magic DR does apply in a few areas in the server, and it can be pretty useful.

It's also fair to say it's pretty much only useful in PvE, and then, more often than not, it's opponents with natural weapons (though the occasional mob has non-enchanted weaponry).