What is the difference between the www folder and the public_html folder?  It appears as if they are repeating the same files.

What's the point of having two then?

Now (or at some point in the past), some software was coded to look in public_html, and other software was coded to look in www. The easiest fix was to make www an alias (soft link) to public_html. There's only one copy of the files -- so don't go doing something stupid like erasing all the files in "www" (people have done it!).

So, "public_html/index.php" and "www/index.php" are exactly the same file -- the same collection of bits on the same place on the disk. Erase one, and you end up erasing the other. "public_html" and "www" are just two different ways (names) for getting to the same place (the directory containing "index.php"). The concept of a "link" (hard, or soft/symbolic) is familiar to Unix/Linux users, but is foreign to most Windows users. It's just a way of giving multiple names to one file or directory. "Remove directory www" would only get rid of the name, leaving "public_html" intact as the only name for that directory, and likewise for removing "public_html" and leaving "www". Remove the last remaining name for a file or directory, and the file or directory actually gets erased.