I think they mention something about wiping 3PO's memory in ROTS. However, Obi-wan says he doesn't remember owning a droid like R2D2. Lucas didn't really care about continuity in the series, it was all about the cash. Don't be suprised to see the final trilogy, no matter how much he denies it.
They did wipe 3PO's mind... but there are STILL enough holes i could drive a tank through it!
Oh well.
I liked it anyway.
Well, he didn't own R2, and really wasn't around him all that much to remember him distinctly from any other astro droids, which were numerous.
Don't know about the third trilogy - the story of the fall and redemption of Anakin Skywalker is over.
If he's gonna do the third trilogy, he'd better hurry. Mark Hamil isn't getting any younger, and IIRC he signed to do them before he left the set of RotJ.