I am reading an O'Reilly book, "TCP/IP Network Administration", and
there is something said which does not make any sense to me. Is there
someone who might be able to explain the meaning behind this:

  TCP/IP CH 6 - Configuring the Interface

 "When networking protocols work only with a single kind of physical
network, there is no need to identify the network interface to the
software. The software knows what the interface MUST be; no configuration
issues are left for the administrator."

  This doesn't make sense to me, because if I set up a machine with an
ethernet card in it, I still have to configure that interface. I tell it
what IP address to use. Even if I only have one ethernet card, and no
other interfaces installed, this is so. Why would they say something like
this? What do they mean that if there is only one physical interface it
doesn't need to be configured?