 Because the webisodes were filmed during the break between seasons,  many of the main cast members had left Vancouver, Canada and could  not appear in them. That is why only characters such as Tigh  (Michael Hogan), Cally (Nicki Clyne), or Tyrol (Aaron Douglas)  appear in them: these are all actors who live in Vancouver already,  and were thus close enough to production to do the webisodes.