I honestly think that his sample "setting bible" may have been one of the most useful campaign-building tools he has ever dropped in this column. I like his ideas for this game - it's the first time that Arthurian-themed roleplaying has seemed appealing to me at all - but that's beside the point.
I think the kind of things that he put in there can really help with player buy-in to the setting you want to create. Tell the players what kinds of cultures are available, what they name themselves, what they look like, how their culture operates, etc. The maps and brief history lesson certainly help bring things to life as well.
I also like that he forces players to think about how their characters were affected by the catalyst for starting the game off. Right from the word go, every player has something to talk about, something to relate to each other with, and a built-in mystery to solve, regardless of cultural background.
Doing a setting bible has been a formula that I've accidentally stumbled across a few times in the games I've run, but I hadn't always used one, and I can certainly say that the games I've run that were most successful were the ones that had the players in on the conceits of the game from the beginning. Nothing helps a game move along quite like characters that are built to be part of the world.
It's less of an issue in kitchen-sink settings like Forgotten Realms, where everything has a place, by definition, but even then, you have people who know the setting inside out, and they want to make sure their characters make sense for that setting. It's also potentially less of an issue in deliberately vague settings like PoLland, but I find that can lead to less player investment in their characters and how they relate to other characters in-game.