I helped digitally convert my local library's microfilm archives, mostly newspapers, but also some really old titles and deeds. Tons of stuff from the 1800s.
If I asked a PhD, "How many Bs are there in the word 'blueberry'?" They'd call an ambulance for my obvious, severe concussion. They wouldn't answer, "There are three Bs in the word blueberry! I know, it's super tricky!"
They are a shorthand for "give me the index of this directory" rather than "give me the first file you find named this." In some configurations, the presence of absence of a trailing slash dramatically reduces the amount of computation an HTTP server must execute before responding to the request.
There's no pirating directly from the source, but there's nothing stopping you from pooling cash from your buddies and setting up email forwarding.