While using dochelp I tried to read the Debian Python Policy but only the text version would open.
Turns out /usr/share/doc/python3/python-policy.txt.gz is shipped in the python3 package but /usr/share/doc/python3/python-policy.html in the python3-dev package.
Since /usr/share/doc-base/python3.python-policy is shipped in the python3 package it seems the HTML documentation should also be.