I was thinking about this last night, and wondered, even thought they have the same root -- from the greek word for foriegner..

i think that barbarous might refer to the pirates of the Barbary coast* (cut throats and not someone you'd want to meet in a dark alley, or all alone at sea) and barbaric-- acting like a foreigner..

it would account for what we all seem to realize is a difference in the meaning of the two words...

*and as to not cast aspersions on the people of barbary-- NY (City) was (and some say, still is) home to many a pirate. Capt. Kidd called it home-- as well as many lesser known pirates. Mostly they stole from the Spanish traders (and the english didn't mind) but eventually, when pick'ins got slim, they raided english ships too. A No-No!