I know what you are saying about Neil Young but no he isn't American just like Michael J. Fox, Mike Meyers, William Shatner, Joni Mitchell, Christopher Plummer, Donald Sutherland, etc., etc., aren't American.
They all went where the work was, I don't blame them for that and certainly wouldn't want to revoke their citizenship based on that.
My Dad was in the Airforce and for the first half of his life and spent almost as much time living outside the country as in it. I think it is up to an individual to decide where they consider themselves to be from and where "home" is for them.
Does this apply to Michael Ignatieff too, or just musicians and soldiers?