Actually, now that the EU is gone, I'm really curious if it was ever revealed to Luke that R2 was owned by Luke and Leia's parents. In the EU, the Dark Nest trilogy (besides being a kind of good/kind of bad story about mind controlling bugs) had Luke and Leia learn about their mother, and that R2 was owned by her (Luke saw a hologram of her and Anakin R2 had, which lead to Leia and Luke finding out about their mother). Its something that's up in the air now, since there was no one alive by the end of the OT to tell them about their mother, and obviously no record of their births.
Unless Obi Wan's ghost came back to give them info, R2's one of the only things that knows about their mother and is still around (I'm pretty sure he was never memory wiped like C-3P0). I mean, some people that knew Padme might still be alive, and I'm sure she's remembered on Naboo, but almost no one knew she was the mother of Luke/Leia. Only Obi Wan, Yoda, Bail Organa (and possibly his wife), and R2 (plus C-3P0, but he got a mind wipe) definitely knew about Luke/Leia's parents from what I can tell. Even Luke's aunt/uncle might not have known who Luke's mother was (they might have known it was the woman they met when Anakin was on Tatooine with her in AOTC, though). I doubt this will be brought up in a movie, but its something I'd be interested in seeing a book talk about.
