Hussar
Legend
As a theory as to why the game itself, as in books and articles, might emphasize world-building as something fun and interesting to do:
It's key to the hobby that running a game be fun. And I think the allure of world-building is a selling point for brand-new GMs. You want to make GMing something with lots of fun aspects to prep time, because otherwise it can be a daunting job. It's a similar principle to 4e design making things easier on the DM: without enthusiastic people running the game, you have fewer players acquired and retained.
Emphasis on world-building is an approach that encourages new GMs to give it a go. It's dangling a carrot of "hey, neat stuff to play with!", emphasizing the creative aspect to make the task more interesting than simply playing referee. Now, I certainly think there could also be some more discussion of how to plot an adventure, or tools to aid improvisational GMing, but world-building is probably a good inspirational hook to get newcomers to try running a game in the first place.
It's not guaranteed success, mind, but I think it's at least more responsible than dangling the carrot of "YOU HAVE THE POWER! THEY LIVE AND DIE AT YOUR WILL!"
And I can accept that. It certainly appears to be the common wisdom. Between sourcebooks, the DMG, Dungeon, and any number of blogs and whatnot, people put world building at the top of the list for starting a new campaign.
Note, I do not equate a lack of world building with improv GMing. That only becomes equal if you assert that all setting creation comes under the umbrella of world building. I disagree with that definition.
I think that the game would be better served if the section on Creating a Campaign in the DMG was organized differently. Instead of putting World Building at the number one slot, put it down in the third or fourth slot. Here's a bullet list of how I think it should look.
- Number one slot would be sitting down with your players and discussing/brainstorming what you want the next campaign to look like in very rough terms - themes, particular issues, amount of combat, that sort of thing.
- Number 2 Background creation of the PC's. Again, you cannot go too detailed here, but more look at the motivations of the PC's. What do they want to do and how can you mesh that with what you want to do.
- Number 3 Flesh out one beginning adventure and how to lay hooks for subsequent adventures.
- Number 4 Start developing those hooks that the players want to pursue.
- Number 5 Start developing broader level setting elements that might be of use. (world building in other words)
Now, I'm not a professional writer and that shows. I'm sure someone else could make that list look a lot better than what I came up with in 30 seconds. But, I think that gets the gist across.