http://i.imgur.com/LypKK8I.png
edit: you're correct, that's the rationale in the pep. It's not why I stick at 79 though, I do it for git log -p, etc.
OTOH, 0x0d definitely counts toward the limit!
In other words, it's a line ending, not a line separator.
http://i.imgur.com/LypKK8I.png