They are probably just checking the user agent.
This worked for me:
#!/usr/bin/perl
use strict;
use warnings;
use LWP::UserAgent;
my $amazon_url = q{http://www.amazon.com/exec/obidos/ASIN/0394756673/r
+ef=nosim/bookreadersre-20};
my $ua = LWP::UserAgent->new;
$ua->agent('Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.3
+) Gecko/20070309 Firefox/2.0.0.3');
my $response = $ua->get($amazon_url);
my $page = $response->content;
my $sought_string = q{offer-listing};
if ($page =~ /$sought_string/){
print "Found it\n";
}
else {
print "No luck\n";
}