Ack! I figured it out. Calibre does not install these tools by default on a mac.
You need to run calibre and go into Preferences->Advanced->Miscellaneous and click "install command line tools".
Source:
http://calibre-ebook.com/user_manual/cli/cli-index.html
I guess Kovid is figuring that mac users are too scared of the command line.

Prove 'em wrong!