Digital content changes over time, in a way other media content does not. Unlike a book, a brochure, a clay pot, or a piece of film, users expect web content to be easily and regularly revised. (Side note: this is why “under construction” pages, so popular in the 90s, with their cute icons of little construction workers, were basically pointless. All digital experiences are, in some way, “under construction.”) Therefore, a well designed digital experience includes, by definition, a maintenance or content management plan — which is a design for how the experience will exist in time.
In short, digital design must account for time. Otherwise, an experience is just posing as a well-designed experience for the sake of oohs and ahhs at launch. Time will reveal it to be a fraud.