Puggo - Jar Jar's Yoda said:
When ESB was produced in 1980, Obi-Wan didn't even know Leia was Luke's sister. I don't even think George knew that.
When they had Obi-Wan deliver the twins to Ben's farm in ROTS, nobody at Lucasfilm stopped and said: "oops, loss of continuity, we can't do it that way".
He only delivered Luke to Owen's farm. ;)