"Fwiw the change of quoting you suggested doesn't actually fix my mistake."

My apologies if the change in quoting was misinterpreted as part of the fix.

The change from //vm to //matrix/vm was the fix.

You had multiple instances of \' and \@ (within double-quoted strings) throughout your post: the quoting change was a cure for backslashitis. :-)

Here's the test I ran prior to posting:

#!/usr/bin/env perl -l

use strict;
use warnings;

use XML::LibXML;

my $file = 'pm_1082058_n4000-small.xml';
my $parser = XML::LibXML->new();
my $doc = $parser->parse_file($file);

for my $vm ($doc->findnodes('//matrix/vm[@type="br"]')) {
    my $version = $vm->findvalue('./release/@version');
    print  'Version: ', $version;
    print  'Wanted:  ', $vm->findvalue('./release/@wanted');

    if ($version eq '7.2.1') {
        print 'Found!';
        last;
    }
}
[download]

Output:

Version: 7.2.2
Wanted:  
Version: 7.2.1
Wanted:  YES
Found!
[download]

As you can see, there's no backslashes here at all (which I find makes the code more readable). The '//matrix/vm[@type="br"]' solution which I posted in my original reply was copied directly from that. If you want to run that test (or modifiy it for other tests), the data I used (pm_1082058_n4000-small.xml) is in the spoiler below.