Trivia: When Jerry and Rachel are in the Circuit City, there is a poster for Disturbia, a movie that starred Shia LaBeouf and was directed by D.J. Caruso, who directed this film.
Trivia: The voice of ARIIA is actually Julianne Moore who went uncredited for the role.
Answer: I think it was to show that Jerry and Rachel maintained a friendship after it all. Also to maybe, maybe hint about some kind of romantic future in the way that Rachel says, "you remembered", when her ex-husband was said to never have remembered Sam's birthday.That's my thoughts - I think it's just to let us know how the characters turned out.