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.
So, is this presenting an implementation detail as well?
I only asked my original question because I thought I was missing something...