Oops! Sorry guys.. need to brush up a little. It's funny cause I recently watched ANH:R in anticipation for ESB:R, lol.
But still I stand by with what I said. For me it always seemed like ol' Ben actually does recognize the droid, he just doesn't admit it.
In any case, R2 isn't referred to as R2D2 in front of Obi-Wan anyway.