http://docs.python.org/py3k/urllib errors out rather than returning an index page for the modules that are part of the urllib package.

This index page could also link to the HOWTO at http://docs.python.org/py3k/howto/urllib2.html

The following packages have the same problem:
xml, http, xmlrpc, concurrent

These ones look OK:
logging, curses, html, tkinter

These index pages don't necessarily need to be linked from the contents page, but they should exist so that manually typed URLs for these packages do something useful rather than erroring out with a 404.