Hi,
As I understand, if your request is
http://www.example.com/index apache searches for a directory
named 'index' and a file called index.html or index.php inside
that directory, using the DirectoryIndex directive to find
the file.
It could be wrong to add 'index' to DirectoryIndex because
without an extension, apache cannot determine the handler
to use, and a file named 'index' without extension will
be confusing so i don't see the point in having a file
called index when it should be easier to call it index.html
If you really need to have a 'index' member in your url then
maybe a rewrite rule or something like that can be
implemented, but again, i don't see the point.