This is a <a href=”http://www.tcpipguide.com/free/t_IPReservedPrivateandLoopbackAddresses.htm”>reserved loopback address</a>. It is there so you can test connectivity.
Not on an AS/400. The documented loopback address is explicitly given as 127.0.0.1 (regardless of standards.) I had quite an enlightening conversation with IBM on that topic a few months ago. The question addresses may simply be used to guarantee no connection for those host names.