Loved the article, I do enjoy that games are allowed to reinvent themselves in sequels in a way that just is not possible in movies or books. Having series defined by general mechanics and themes rather than a long form narrative is one way that games are distinctive from many other forms of media, it isn't entirely unique.
Series such as Discworld or Redwall function in very similar ways to The Elder Scrolls. They are an array of different stories, some placed hundreds of years apart, bound together by the common elements of the world itself. The worlds history, lore and magic tie Skyrim to Morrowind in much the same way they tie Guards! Guards! to The Colour of Magic.
To some degree, yes, books and movies have reached a sort of plateau in terms of presentation, while games can still continue to evolve and improve, the fast and loose sequel structure many game series use is not particularly unique to gaming.
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There was a minor thing though that bugged me.. Probably more than it should have; using the updated Portal ending as an example for a Retcon.
It isn't retroactive when there is nothing you are going backwards from. The game ended with you blacking out in a parking lot as debris fell all around you. There was no particular implication that you actually truly escaped. Had Chell gotten up and walked through the gates, and then the ending was changed to have you dragged away, then it would be a retcon. Things would be erased, or changed. But that didn't happen, which is understandable due to Chells escape method, standing next to a massive explosion. The view of the parking lot was always meant as sort of hollow victory, that the act of overcoming your jailer had left you physically incapable of making the final steps to freedom.
However with no further continuity (Past the point of Chell blacking out) you can't really call adding an extra 5 seconds at the very end an example of retroactive continuity. Yes, the addition was retroactive, coming years after the games release, but in terms of the continuity that moment was still the present. There was nothing after that. Any moments taking place in the present continuity are by definition not retroactive.