Not really. Even for non-cruise line tours, it isn't that uncommon for the ship to wait. Sometimes even for an hour or more. I have personally watched it on Disney. I have also watched videos where a captain announces he will confine a couple to their room for the remainder of the cruise after they were late a second time on the same cruise, but he still waited. That probably leaves the impression for some cruisers that there is a cushion, despite every line saying over and over again that there is not.
That said, it is stupid to not assume the ship will leave without you and not build in padding, which needs to be bigger the farther you go from the ship, as well as being prepared to travel on your own if you don't make it back in time. Being prepared includes for cruise-sponsored excursions, because you never know what may happen when traveling.
These people claim to be very experienced and are crying about being left in Spain? It really shouldn't be the end of the world if you are an adult and have done the smallest amount of research on how to travel in a foreign country. "Richard’s eyeglasses and both their spare hearing aid batteries and phone chargers on board." Sounds like a rookie mistake, not an experienced traveler. I wouldn't be so judgmental if they didn't have the main-character syndrome that permeates too much of society these days.