From a practical point of view, regardless of the scope of the original question, this is the kind of scenario where you'd really want the restriction. More than a simple administrative task it's a dangerous attack vector to allow any user to launch your httpd or DNS.
That being said, check out capabilities(7) in Linux. You can grant an executable the privilege of binding to a low port when run by non-0 uid through setcap. This is a good compromise.
