title_body: How does Project Gutenberg structure their epubs?
upvoted_answer: Looks like indeed this was created with some automatic tool. I was snooping around the file in the Miscellaneous folder and found content.opf which has a bunch of traces of this Split on p operation showing up in the comments along with a relatively uniform chunk size.
  
  Furthermore I emailed them about an error in the table of contents and got this response...
  
  David Widger via RT
  7:05 AM (3 hours ago)
  Hi jxramos,
  
  I find that this was one of the early PG productions which were only in the
  ASCII format and had no accompanying html file made by the producer of the text
  file. The html file listed with this ebook was one autogenerated and these are
  often quite unsatisfactory.
  
  A much better PG edition is:
  
  http://www.gutenberg.org/files/8300/8300-h/8300-h.htm
  
  The html file was manually produced and the mobile viewer files appear
  satisfactory.
  
  I would refer you to PG #8300
  
  Regards,
  
  Project Gutenberg