I haven't seen my copy of "Castle Falkenstein" in over a decade (I think it was actually lost in a rather hasty house move at the start of 2002) years.
One of the things I do remember about it was the was the first half of the book was written an a travel journal. It was literally written from the perspective of someone writing their diary in a strange reflection of our own world, pulled there by magic and now interacting with the people and places of the pseudo-Europe with their summoner as a guide.
I've seen this sort of things in children's books, James Gurney's "Dinotopia" comes to mind, so do those "Dragonology", "Pirateology", and other "-ology" childrens books that describe a secretive world in easily digestible terms...in truth, this sort of conceit is a literary tradition that has gone back to at least the Victorian era. It's just uncommon to see this presentation in a game book.
Jeremy Keller's "Chronica Feudalis" pulled off the same technique really well a few years back. I've got a PDF of it floating around and occasionally look back to it.
When it's done well, the author's voice can add a sense of perspective to a work. It provides an insight into the game world through the mechanisms of play, rather than keep the two separate. But it's a delicate style to write, and as a reading style, you have to be in the mood otherwise it can be a bit grating. Still it's an intriguing idea.
I've already made the decision to split Walkabout into a generally system agnostic travelogue/setting guide, and a fairly setting agnostic system. The fusion of these two parts forming the whole game (with a possibility to add new setting expansions in the for of new travelogues, or in-setting artefact textbooks).
But it struck me that it could be an interesting idea to develop the rulebook as an in-setting artefact as well. Perhaps with the fall of wireless communications, new entertainments have developed in the post apocalyptic world. Perhaps dice as a mass produced commodity are not as available in the shattered future as they are now (that's convenient because Walkabout uses tokens drawn from a bag rather than dice).
It's just an idea that I'm toying with.