Looking back over the times that the page has been submitted to Hacker News, it's almost an even split between with 'index.php' and without.

It's an interesting question for CIS URLs whether a url-path with an empty final component, that duplicates a url-path with an actual 'index' component (of some kind), is to be taken as the primary or the secondary form. When a site has 'index.php', 'index.html', 'index.gopher', 'index.gemini', and others, the question is whether the container is the same as the index file.