Agreed; lthough the full behavior is more complicated than that
- unless -rpcallowip is specified, it binds to localhost 
- if one or more -rpcallowip and one or more -rpcbind is specified, bind to those specific addresses
- if one or more -rpcallowip and no -rpcbind is specified, bind to all interfaces

But listing all of that in the command line options help is too verbose.