> FWIW, you can do the same on a Linux box, i.e. setup the host name
> and domain to some completely bogus values. And as David pointed out,
> without also updating the /etc/hosts on the Linux, you always get the
> resolver error with hostname -f I mentioned earlier on (which does
> a DNS lookup), so there's no real connection to the DNS system on
> Linux either.

Just to clarify here: there isn't anything special about
/etc/hosts; it's handled by a pluggable module which performs
hostname lookups in it alongside a similar module for the DNS.
glibc's Name Service Switch combines the views provided by the
various modules into a single byte-oriented namespace for
hostnames according to the settings in /etc/nssswitch.conf (this
namespace allows non-ASCII bytes, as the /etc/hosts examples
demonstrate).

http://www.kernel.org/doc/man-pages/online/pages/man5/nsswitch.conf.5.html
http://www.gnu.org/software/libc/manual/html_node/Name-Service-Switch.html

It's an extensible system, so people can write their own modules
to handle whatever name services they have to deal with, and
configure hostname lookup to query them before, after or instead
of the DNS.  A hostname that is not resolvable in the DNS may be
resolvable in one of these.