Where the protocol is http and the port is 80 the :80 can be omitted from the URL.

Where the protocol is https and the port is 443 :443 can be omitted from the URL.

See the following RFC for information on dropping the port from the URL when the default port is used: -

http://www.ietf.org/rfc/rfc1738.txt

Also see the following for the default port for HTTP over TLS: -

http://www.ietf.org/rfc/rfc2818.txt