Varnish seeming to not respect mod_expires and mod_headers expires

[ntwrkd]

I read the tutorial at
http://varnish.projects.linpro.no/wiki/VCLExampleLongerCaching which
states that Varnish should respect the Expires headers; however, it
doesn't seem to be inherited by my implementation.

I have a pretty standard config
backend default {
.host = "127.0.0.1";
.port = "80";
}

sub vcl_recv {
  if (req.url ~
"\.(jpg|jpeg|gif|png|tiff|tif|svg|swf|ico|mp3|mp4|m4a|ogg|mov|avi|wmv)$")
{
      lookup;
  }

  if (req.url ~ "\.(css|js)$") {
      lookup;
  }
}
sub vcl_fetch {
        if( req.request != "POST" )
        {
                unset obj.http.set-cookie;
        }

        set obj.ttl = 600s;
        set obj.prefetch =  -30s;
        unset obj.http.Server;
        set obj.http.Server = "Apache/2.2.10";
        deliver;
}