Bungie, the Halo developers, as well as many other developers follow this philosophy. How can you take 30 seconds of fun and repeat that throughout the entire game? That's what many studios strive for.
That's true too, but what I meant was more specifically for MMOs (and games that have the player move in similar ways) - any bits of fun in the game should be not more than a 30 second drive/walk/run from another one.
Imagine, for instance, a map of Elwynn Forest (if you've played WoW) and construct a graph over it of all the quest-related things to do or see - none of them should be more than a 30 second run from the nearest neighbor. Whether this is actually the case is an implementation issue :)
