How does this actually happen though? Is this simply a case of people leaving the standard "apache index page" turned on or do this many people actually publish links to their SQL files someone crawlable?
Usually a combination of the Apache index pages, dumb server setups, and being people being lazy, careless and/or forgetful when they dump a database to disk.
Also, sometimes an index.html file is accidentally removed, causing (brain-dead installs) to suddenly reveal the contents of a directory, eg. http://shahinfosoft.com/
