Okay, let's get something straighted out here:
I have been using iOS 6 since the first developers release. This problem IS fixed in iOS 6. It is still a problem in iOS 5 but you only have three more days before you get the update that FIXES the problem.
Perhaps something is wrong with you file. The way audiobooks work, is you have a "chapterized" or "bookmarked" file. This is why audiobook files are generall M4B (B, not M4A like many of your songs) or audible's file type aax. These files store information in a type of hierarchy, the file name (book name), bookmarked places (your chapters).
So the interior of these files would look something like this:
A Dance with Dragons
- Chapter 1: Prologue
- Chapter 2: Tyrion
End of audio File
or just
A Dance with Dragons
- Prologue
- Tyrion
- Daenerys
It all depends on who made the file. So, personally, whenever I get an audiobook, I break the file open and re-encode it to my standards. But in iOS 6, both basic audible files, other audiobook files, and my own personally created audiobook files show the chapter names as they are within the file(s) you have.
You have to understand, Apple isn't like other companies that push out a full update to fix one minor problem like this audiobook issue. If you are really that concerned with having audiobooks by chapter, you can find other work-arounds like breaking chapters apart and just putting them into an album (named as your book) with the chapter names as the file names.
But like I said, you only have 3 days until you can get iOS 6 and the problem is fixed anyway.