I forgot completely, but in Python3, Issue5418 had already added
support to addinfourl. It is now possible to write code like

import urllib.request

with urllib.request.urlopen('http://www.python.org') as req:
    res = req.read()

But yeah, unlike normal file objects, it not a strict requirement for
closing those objects as they will be closed when socket connection is
closed.

This is available only 3.x series and I think, a documentation update
should be fine and this report can be closed.