the pages i have made do not link to the index directory, i was wondering the same thing,
the link created by the spider/indexer is a link to the directory not a html file, phpdig is finding the index of a folder and displaying it as a link:
see here is an example i have taken from the site:
http://www.robotstxt.org/wc/
the '-' i get is linking to pages the same as the above link:
so if i search my 'cars' html page on my site i get results that link to addresses like:
(these are made up examples)
'cars/cars.html' and 'cars/'