Files attached to nodes are never deleted from server even after they're removed from the node (and that edit is saved), Drupal 7 I've noticed something strange on my site: after attaching a file to a node (via the regular file field), that file never gets deleted from the server.  I remove it from the node, save that change, but I can see the file is still on the server.

This makes replacing files very difficult, because when a user tries to attach a replacement, the file name has the "_0" or "_1" suffixed to it (since the original file is still on the server and that makes the name a duplicate).   That means that we would need to find all links to the file and edit each one to match the new file name/url.  It's a total mess.

I'm looking online and nobody seems to have this issue -- the files ought to be deleted from the server once they're removed from the node.

Any ideas why this may be happening in my case?  I'm not sure where to start looking.  Certainly the 'File system' configuration page has nothing of that nature as an option that may have been checked.  And the field options themselves seem to not have anything of that nature I may have inadvertently set.  Any other ideas?
I got it!  It's a revisions thing.  I guess it makes sense.  If you have revisions enabled for that content type, it keeps all your old files on the server (associated with old revisions), so replacing a file definitely is harder.  If you try to remove it and add it again to the node, the name/link is updated, as I mentioned in my question.  Since a file with that name is kept on the server and there is a name duplication, it adds those "_0", "_1" etc suffixes to future uploaded versions of that file's name.

I understand why this is happening though, since the whole point of revisioning is being able to revert to any past version of the page.

The work-around is that you can actually delete the old revision from the 'Revision' or 'Moderate' tab (if using Workbench Moderation) that contained the file you're trying to replace.  Then upload it again, and the name should then match without you having to go back and edit any links pointing to that file.

Hope that makes sense and that it helps somebody else too!