You didnt' do anything wrong (except listen to me ;) )... I gave you bad code.. the last comma should have been a colon like:
<?php foreach( $_POST as $pkey => $pval ) { ?>
<?php echo(str_replace("_"," ",$pkey).": ".(str_replace("\n","<BR />",(is_array($pval)?implode(", ",$pval):$pval)))); ?>
<?php } ?>
(I also updated the original post to be correct)