Finally, an answer!

So Why, Exactly, Do C3P0 and R2-D2 Not Remember Obi-Wan Et Al In STAR WARS EPISODE IV: A NEW HOPE?
E! Daily News interviewed Star Wars creator George Lucas and finally got an answer on the mystery surrounding what R2-D2 and C-3PO should and shouldn’t remember of their adventures in the prequels.
A slight SPOILER warning is given for what Lucas had to say…
“Well, one, his brains have, his memory system has been erased and so has R2’s. So, they don’t remember anything from the first trilogy. I’m telling you something from Episode III, but I shouldn’t be telling you that, but I think most of the fans already know that.”