I heard that only C3PO gets his memory erased because R2 can "keep a secret"....whatever.....but anyway, wouldn't R2 recognize Yoda? I mean just cause we don't see them together(or at least haven't yet) doesn't mean they're not together. Whatevz, all the Jedi are lying sacks of wookie's nut sweat. They got what was coming to them. OB1 remembered the droids. How are you gonna forget the first gay, gold droid in existence? He just wasn't done formulating his lies yet.
Ok simple... Obi Wan knows that C3PO's memory was erased and kind of elbows R2D2 about not knowing the droids. Look at his expression when he says "i dont ever remember owning any droids before"
He looks at R2 that way because he was supposed to not remember Obi Wan.... R2 in episode 3 will escape from his mind being wiped.... SWWEEEEEETTTT.....
He never owened them, and how many droids out there look the the 2 of them??? lots, just because you see a red focus does not mean if you see another one a year later it is the same one.
he does not realize it is the same droid till R2 plays the message.
I think they only wipe c3po's memory and not r2's
Another point to make is he was unfinished and Silver when he worked for OWENS FATHER not Owen.
Remember Owen and Beru were kids when C3p0 worked for them. He was also silver and unfinished which made him a very simple droid. When Owen finally got him the protocal droid didnt talk to Owen that much except for the whole Bachi and moisure evaporator discussion which can also fit in because he worked on that farm but just dosent know it was that particular farm with the memory erase.
when obi says "hello my little friend" etc. it seems very personal....just too boring to explain to luke....he could have said "yes, i didn't own these droids, but someone i knew did. I had one that was kind of similar, only red, and it didn't have a body, just a head, and it sat in my jedi fighter" etc. etc.....but it was just too boring to explain...as, indeed, it is now...