I think it might be a slightly different underlying model for the way things
are done. VSS uses checkout, modify, checkin. A copy, modify, merge simply
modifies the copy that you already have, noting which version it is, and
then merges it when you ask to check it in. It's a fine point, and I'm
probably not explaining it very well. But even with that, it seems like a
stretch to call it a new feature.

All guessing on my part, simply from information in your post.

Joe