I would have loved to have had Ewan McGregor in the movie but it was just a matter of storytelling. The original relationship with Obi Wan — obviously if Alec Guinness were still with us that would have made sense. But we never saw Luke ever interact with the Ewan version of Obi Wan, so there's less of the emotional connection and it might have been a little odd. ... so it made sense that Yoda be the one that comes back and kicks [Luke's] butt a little.