I don't know what to do about this and I claim no expertise in .htaccess rewrite rules so if someone knows how to work around this please help.
With Drupal installed (apache 2.2.22 / php 5.4.9) trying to navigate to any of these paths throws a "500 Internal Server Error". If I remove the drupal folder altogether from the webroot directory, the pagespeed statistics page is shown.
PS: This is an already known issue with many CMSes and pagespeed out there, but so far the official stance of pagespeed developers is that it is the responsibility of each respective CMS to provide a solution:
Issue 597: Can't access to the stats pages other than from localhost