Isn't it? Logically, just as enemies respawn, so to would certain types of quests (unless every enemy in the world has become so terrified of you that they stop coming out of their lairs). Goblins will eventually threaten villages again. . . because that is what Goblins do. Necromancers will start looting graveyards, or killing beggars to turn into zombies. . . because that is what Necromancers do. Bandits will rough up small settlements and waylay merchants, because that is what Bandits do. Vapires will slip into villages to drink from the inhabitants, werewolves will threaten villages and make the inhabitants hold up in terror in their huts. . . because that is what vampires and werewolves do. And villagers will seek aid from a hero when they cannot master their monsters themselves. . . because that is what threatened village people do.
I believe you misunderstood what he said. What he meant is, after finishing all quests, he can still explore the world, and find things, and fight things, and talk to people, etc because containers respawn, creatures respawn, and NPCs have generic dialog. I guess adding a "save my town" dialog line wouldn't be an issue, but that "setup" isn't necessary, if what you want to do is fight things and find things.
I also think you are using the wrong term: a quest is something that has stages to it and allows you to make decisions along the way. What you describe is more of a random encounter, to which is what the other poster was referring: even after the story ends, you are guaranteed random encounters because of respawing assets.
As general rant...
There's more than one way to look at this from the now cliche "immersible living and breathing world " perspective.
For example, how immersive is it to find the same 2-3 small towns always being attacked by different creatures/NPCs over, and over, and over again, and they not being able to defend themselves and needing your help?
In a
role playing game, I want to have the choice to tell them the first time, or the 2nd or 3rd time: "hey, you better learn how to fight or defend yourselves, I am not doing it (again)" or "I may not be here in time next time", and next time I come around, the village is either wiped out, or now they can defend themselves. NOW you have a bona fide role-playing situation with true consequences, but effectively there will be no need to summon you again, and therefore the quest ends.
Personally, if I want to be the hero and play the same scenarios over, and over, and over again, I just replay the game over, and over, and over gain. Of course, I make mods for my game even as I play the first time, so even after various replays making different choices, my game still has something different in it... I rarely download other people's mods, but I download quest mods, because they give me a fresh perspective
I guess the idea of the never ending game was born out of MMORPGs. A single-player
game may not effectively end, like Oblivion, but the
story in a role-playing game will end, unless something is added to it.