The reason is because of Ubuntu's no open ports policy, thus it cannot be enabled by default
There *is* a GUI way System->Administration->Networking "General" tab click "Enable service discovery" -- /etc/init.d/avahi-daemon is useless https://launchpad.net/bugs/56426 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
