How do I transfer audiobooks from iPod Touch to iTunes?
If I remember correctly, iTunes doesn't let you copy media from your iOS device to iTunes; likely to prevent piracy. If you have purchased the audiobooks from iTunes, you should be able to download them back. If not, which it appears you can't, you may have to contact Apple Support.

Edit:


  Apple told me that if the author has made any edits to the book, they change the serial number and they won't allow you to re-download-even though I purchased the book!


The only thing I could come up with that made any sense is that you can't update content in iTunes. Music, Books, TV Shows, etc. are usually never changed when they are published. If the author of these audiobooks made some changes to it, they would probably have to submit a new book. This happened to me once when a music artist added a few songs to their album. He created a new album and took the other one off the store.