You can retrieve submitted values across all pages from $form_state['storage']['submitted']

You can retrieve submitted values across all pages from $form_state['storage']['submitted'].

Note that this represents values from past pages and not the current page. Here is the code I use to get them all (past & current) page values into a single array:

$values = _webform_client_form_submit_flatten($node, $form_state['values']['submitted']);
$values += $form_state['storage']['submitted'];