How to print preprocess_html variables in page.tpl
Yet another, perhaps simpler, to add variables to multiple templates, is too use an earlier hook_preprocess


  Preprocess theme variables for templates.
  This preprocess function is the first in the sequence of preprocessing and processing functions that is called when preparing variables for a template. 


e.g:

/**
 * Implements hook_preprocess
 * @param $variables
 *   The variables array by reference.
 * @param $hook
 *   The name of the theme hook.
 */
function THEMENAME_preprocess(&amp;$variables, $hook) {
  switch($hook){
    case 'html':
    case 'page':
      $variables['foo'] = 'my special variable';
    break;
  }
}


See also: template_preprocess