macOS Server firewalls port 80

Not only does macOS Server start an httpd on ports 80 and 443, it also apparently sets up firewall rules so that if you are not running the supplied server, you cannot receive anything on the ports. This seems a bit anti-social; does anybody know why? A quick fix is to remove the offending lines from /Library/Server/Firewall/Anchors/combined_anchor.txt and reload the firewall with pfctl -F all.