Here's a crude (but accurate) method of finding the differences. Reconstructing the required result is left as an exercise for the reader:)

#! perl -slw
use strict;
use Data::Dumper;
use Algorithm::Diff qw[ diff ];

my $given = {
          'Subtype' => [
                         {
                           'url' => 'http://www.google.nl/',
                           'title' => 'testNL'
                         },
                         {
                           'url' => 'http://www.google.be/',
                           'title' => 'testBE'
                         }
                       ],
          'name' => 'test1'
        };
my $retrieved = {
          'Subtype' => [
                         {
                           'url' => 'http://www.google.nl/',
                           'title' => 'testNL'
                         },
                         {
                           'url' => 'http://www.google.be/',
                           'title' => 'testBE'
                         },
                         {
                           'url' => 'http://www.google.de/',
                           'title' => 'testBE'
                         }
                       ],
          'name' => 'test2',
          'type' => 'test2'
        };


=pod

The result should be:
$result = {
          'Subtype' => [
                         {
                           'url' => 'http://www.google.de/',
                           'title' => 'testBE'
                         }
                       ],
          'name' => 'test2',
          'type' => 'test2'
        };
=cut       

print @$_ for map{ 
    @$_ 
} diff( 
    [ split "\n", Dumper( $retrieved ) ], 
    [ split "\n", Dumper( $given )     ] 
);

__END__
 8:37:10.53 P:\test>344057.pl
-9                         },
-10                         {
-11                           'url' => 'http://www.google.de/',
-12                           'title' => 'testBE'
-15          'name' => 'test2',
-16          'type' => 'test2'
+11          'name' => 'test1'
[download]