I think 1, 2, and 3 could all fail. Cpan could only be considered more static in that you would expect it to be up if you just installed a module from cpan, but really the ftp and http servers aren't related.
in reply to Accessing the net during module installation
A better approach might be to go to a site and follow the first link, vs a named link, but I believe following a particular named link is a test.
Whatever the case, the install should prompt the user before *any* communication outside of the machine. The network policy at my work is very strict. For example, there is absolutely no external email access allowed, including webmail. If an author decided to bounce a test off of mail.yahoo.com, it would be a direct violation of our network use policy, without me even being aware of it.