Are you confusing HTTP with CGI? CGI is a specification allowing communication of a HTTP request and a HTTP response between two programs by means of a combination of environment variables, STDIN, STDOUT and STDERR. mod_perl doesn't set or use those env vars, and I doubt that mod_php does, so neither use CGI at all.
Comment on Re^4: Another prediction of Perl's demise
Not for handlers, no. It does when you run Perl code through the perl-script handler. Also, the standard filehandles are never directly connected to the browser, though you can usually pretend they are.
"There is no shame in being self-taught, only in not trying to learn in the first place." -- Atrus, Myst: The Book of D'ni.