Module newbie mymodule _action_info_alter problem

How come this works

function mymodule_action_info_alter(&$info) {
// Make the "Block current user" action available to the
// comment insert trigger. If other modules have modified the
// array already, we don't stomp on their changes; we just make sure
// the 'insert' operation is present. Otherwise, we assign the
// 'insert' operation.
if (isset($info['user_block_user_action']['hooks']['comment'])) {
array_merge($info['user_block_user_action']['hooks']['comment'],
array('insert'));
}
else {
$info['user_block_user_action']['hooks']['comment'] = array('insert');
}
}

And this doesn't

function mymodule_action_info_alter1(&$info) {
// Make the "Send email action" action available to the
// comment insert trigger. If other modules have modified the
// array already, we don't stomp on their changes; we just make sure
// the 'insert' operation is present. Otherwise, we assign the
// 'insert' operation.
if (isset($info['system_send_email_action']['hooks']['comment'])) {
array_merge($info['system_send_email_action']['hooks']['comment'],
array('insert'));
}
else {
$info['system_send_email_action']['hooks']['comment'] = array('insert');
}
}