Using a dyn.com dynamic host name with an AirPort device
Quoting from the page referenced in the question:


  Note on DynDNS Free and DynDNS Pro: We currently do not support Wide Area Bonjour on our DynDNS Free and Pro services. You must use Dyn Standard DNS with your own domain name for this to work properly.


So it won't work with dynamic dns.com addresses.