I assumed that as this section of code is actually part of the Joomla libraries it was pulled from the Joomla framework -- which means that using a override in a admin template could call this function and set CDN in the template because he wants to use a completely different version of jQuery or other core script.  This would override behaviour set in the cofig, because the template developer sets it.  I approached it the same as the team  have approached debug calls...either or approach