GL has referred to this matter as 'unimportant', though it is unclear whether he was directly dismissing the apparent anomaly or not. Whether we will see why the droids appear so ignorant is yet to be seen.
R2 could well have recognised Tatooine and just not mentioned it. That both those droids are capable of lying is well established.
there is nothing to suggest that r2 has had his memory erased, if anything when he lands on tatooine it is though he has been there been before, remember the way in which he and 3po seperated, r2 seemed to have a much clearer idea about where to go, secondly it would seem unlikely that droids forget, he remembered ob1 afterall.
The memory wipe is another one of those points that make me wonder what the heck these droids are doing in the PT. If this really happens they are ONLY eye candy and merchandise potential. GL better make this work.
And indeed the droids were the 'peasants' in the OT. If they are an integral part of the PT, I don't know. Not too fancy what I've seen so far. Just excuses to show them droids.