Eg: http://www.example.com/path/to/url/ should open to the first specified of the the specified default objects, typically index.html index.shtml index.php index.php, or similar. This is defined in your Apache conf file, or locally via .htaccess.
If you want to refer to a specific non-index page, you'd specify http://www.example.com/path/to/uri/somepage.html
So, regarding the "index.html" portion: The index is the default. There's no point having a default if you have to specify it, and there's no point specifying it if it's the default.
If I change my file formats from HTML to SHTML, .jsp, .php, etc., the URL changes.
If I change from files to directories for every possible URL instance, the URL changes.
The user shouldn't care.
So, is this presenting an implementation detail as well?
I only asked my original question because I thought I was missing something...
If you'd started with the 'document'-.'html' naming convention, you could use any of numerous webserver hacks to preserve this illusion. How you request something has little to do with what the server does to satisfy your request.
What I was distinguishing earlier was the distinction between 'return default index of this level of the path' and 'return a specific document from this level of the path'. Specifically indicating 'index.html' is a tad gauche.