Maybe Chewie was part of the plan all along. Perhaps it will play out that he owes Obi a life debt for saving him from something in Episode III so Obi tells him to be in that cantina with a ship in 18 years to help begin a new hope for the galaxy. Perhaps Obi-Wan and Yoda forsaw it. I know its a stretch but....
Actually, on second thought GL probably has us all chasing our tails on the speculation with all of the info released so far completely false. Wouldnt suprise me, since I believe that this is the movie that 99% of the fans have waited to see since the release of The Empire Strikes Back and we found out who Vader really is.