The second problem plaguing most flavors of unix is the abundance of insecure services that any network user can access. Relying on twenty year old protocols like telnet, rsh and rcp, it puts users at risk from transmitting secure information via insecure channels. Further, installing services for calender management, remote file system sharing and other network features, they open up a user's machine to a world of potential problems. In many cases, these services are never used and often forgotten. Not only is this solution a better practice in general, it is more in tune to how the world of computers work.
Experienced administrators are familiar with their systems.
They know the ins and outs, what services are required and how to tweak the system. On a closed system, they would have the knowledge to open the necessary services in order to meet user demands. On the flip side, newcomers to Unix are not familiar with the details. They do not know that you can shut off NFS, FTP and other services on many home systems. This lends to the problem of open and insecure machines litering the Internet.