It is not so much so that they added stuff. More that they left it out (due to time constraints, I presume). By doing so they made the story less "rich" in background and depth. Because of that there are large parts of the story that remain unexplained in the TV series.
I think this is what made Babylon 5 special: it was written from the ground up to be televised and to have a 5-season story arc. Straczynski had to force the producers to stick to that idea right to the end, but it paid dividends in the quality of the series, I feel.