Why?

That question was asked now ~10 years back. The answer was: to check if the submitter is using an random open proxy server from the net to bypass their IP filter.

From the code

    # If we don't have an IP address, it can't be an open proxy.

And scanning commonly known proxy server ports.

    my $ports = $constants->{comments_portscan_ports} || '80 8080 8000 3128';