Now I'm completely confused. My entry disappeared, so I rewrote it, then the original appeared, so I tried to delete the second, and both disappeared. Once more unto the breach, dear friends ...
As far as I know, "duh" was first used for the sound a fool makes at the beginning of a pitiful answer: "Why did you pull the bull's penis ?!!" "Duh, I thought it was a cow". The fool cannot see the painfully obvious. This evolved first into the imitation of the fool in the incredulous "Duh, you thought it was a cow ?!! ", and finally into the expression of disdain to someone who can't refrain from stating the painfully obvious: "It's raining." "Duh, you think?" So "Vraiment ?" and "Ah bon ?" (delaMancha) would serve perfectly well. I have never heard the combination "No, duh", but since the use of "duh" is strongly age dependent I may simply be out of the loop.
I give up. Let this stand as is.