Install problem civicrm with wordpress
In looking at this further, it appears on any external call or via cron, in version 4.7.0 CiviCRM looked for the settings file ONLY in the directory wp-content/plugins/civicrm if the CMS was WordPress.   

In 4.7.1, this was changed to look in both '//uploads/civicrm' and '//plugins/civicrm'

Therefore on 4.7.0 with the civicrm.settings.php file in wp-content/uploads/civicrm you could get the failure on cron that you describe.  

I would try updating to CiviCRM 4.7.1