I tend to disagree. Yes slammer hit 1433, but in my humble opinion you do not change port numbers due to security issues. If you do read about slammer, the patch for the slammer security issue was released more than six months earlier. Slammer did much damage to to unpatched systems, not due to default port numbers.

There are still valid reasons for specifying port numbers. The two most common cases I've seen is routing access through a firewall (were all ports are closed by default), and access to named instances from clients who don't understand instances (by using IP and port number).