yeah - they really screwed up on the R2 bit IMO. if R2 was so high tech then, why was he so relatively low tech and slow moving 20 years later?
i guess it is just a movie, so we shouldn't pick on incongruities, but don't you think that Obi Wan (episode IV) might have remembered C3PO and R2 considering how much time he spent with them in episodes I,II,III? that part was never explained away.