Alec Guiness was a great choice for Obi-Wan. He was an acting powerhouse. The line and delivery of "Obi-Wan Kenobi? Obi-Wan... now that's a name I've not heard in a long time... long time" indicates that he has all but forgotten his old life. Not that he hasSpoiler: Rebelschopped a former Sith down back when Luke was in high school.
Semantics. Ahsoka and Anakin never owned R2 either, to the best of my knowledge, yet they get filled with emotion when they see him. Also, Kenobi has no compunctions about telling Luke that he was a Jedi, so hiding that he knows R2 seems more than a bit ridiculous. If the OT was written like the PT, Clone Wars series, and current canon, the line would likely have been more akin to, "I don't recall ever owning a droi-oh hey, R2! We're old war buddies! He even saved your father's life quite a few times. What are you doing here?"