I was just watching the trailer again (still looks great), and although it is unlikely, Obi-Wan's one line in there really sounds like Ewan McGregor to me. Who knows, with some of the other cast returning (at least for the theatrical run), but if it isn't - it sure is a good sound-alike.
Again, this really looks pretty nifty. I think Lucasfilm (and Hasbro) could have a real winner here with a weekly series. Hopefully it turns out as good as it looks so far, because it would be really cool to have a weekly dose of "new" Star Wars to look forward to.