'The $19.99 fee dates back to when Apple used to charge for Mac updates. 'Apple has kept OS X 10.7 Lion and OS X 10.8 Mountain Lion available for customers who have machines limited to the older software, but until recently, Apple was charging $19.99 to get download codes for the updates,' notes MacRumors.
Mac OS X Lion and OS X Mountain Lion can now be downloaded for free from Apple's website.