You don't need a full sort, all you want is to put the domains in the proper buckets. Here's my solution:

#!/usr/bin/perl

use strict;
use warnings 'all';

my @regexes = map {qr /\.$_$/}
    qr {co\.uk},
    qr {com},      # No need for the [\w\-] prefix.
    qr {pl},
  # qr {uk\.com},  # This one already gets grabbed by \.com
;

my @domains = qw {
    foo.com
    weirdext.za
    bar.uk.com
    blah.co.uk
    perl.pl
    zzzz.co.uk
};

my @buckets = map {[]} @regexes, 1;

DOMAIN:
  foreach my $domain (@domains) {
    for (my $i = 0; $i < @regexes; $i ++) {
        next unless $domain =~ qr /$regexes[$i]/;
        push @{$buckets [$i]} => $domain;
        next DOMAIN;
    }
    push @{$buckets [-1]} => $domain;
  }

print "$_\n" for map {@$_} @buckets;

__END__
blah.co.uk
zzzz.co.uk
foo.com
bar.uk.com
perl.pl
weirdext.za
[download]

Abigail