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.
These episodes occur during the four month time period between the end of season two of the main series and season three.
None of the cast and crew involved with the webisodes actually got official credit for it, and this led to a legal battle between the Writers' Guild of America and NBC/Universal about how to handle internet-based content. Previously the internet-only content that TV series produced tended to be little more than extended trailers for the series, but Battlestar Galactica made an actual "bonus episode" which was a serious attempt to make an extra episode and actually advance the plot, which led to serious concerns about payment for them.
Anders is mentioned in one webisode, so we discover he got over his pneumonia and has survived.
The writers consider all 10 episodes to actually be just one "episode" (albeit only half an hour long) that got cut up into 10 pieces, rather than 10 separate little stories.