Custom Placeholder Module
The user account form stuff is one level up in the account container. For the name and email you can use:

$form['account']['name']['#attributes']['placeholder'] = t( 'Username' );
$form['account']['mail']['#attributes']['placeholder'] = t( 'Email Address' );


The password is slightly more complicated, as the 2 inputs are created in a process function. You'll need something like:

function MYMODULE_form_alter(&amp;$form, &amp;$form_state, $form_id) {
  ...
  if ($form_id == 'user_account_form') {
    ...
    $form['account']['pass']['#process'][] = 'MYMODULE_process_password_confirm';
  }
  ...
}

function MYMODULE_process_password_confirm($element) {
  $element['pass1']['#attributes']['placeholder'] = t( 'Password' );
  $element['pass2']['#attributes']['placeholder'] = t( 'Confirm Password' );
  return $element;
}


See form_process_password_confirm() if you're wondering where 'pass1' and 'pass2' come from (it's one of the default process functions for a password_confirm element as set in system_element_info()).

It'll be the same sort of thing for the slider, but without knowing where that slider comes from (module, custom code, etc) it's difficult to say what the code should be. At a guess based on the input name's you're trying to target:

function MYMODULE_form_alter(&amp;$form, &amp;$form_state, $form_id) {
  ...
  if ($form_id == 'views_exposed_form') {
    ...
    $form['commerce_price_amount']['#process'][] = 'MYMODULE_process_commerce_price_amount';
  }
  ...
}

function MYMODULE_process_commerce_price_amount($element) {
  $element['min']['#attributes']['placeholder'] = t( 'Min price' );
  $element['max']['#attributes']['placeholder'] = t( 'Max price' );
  return $element;
}