Comment 13 for bug 576255

Having conffiles be deletable is a feature. Yes, it would be nice if dpkg was move verbose about it (perhaps listing every deleted conffile with a "not reinstating deleted conffile /path/to/file" during installation?), but changing the behaviour to silently restore deleted files breaks some pretty fundamental assumptions about dpkg conffile handling.

"Not there" is a valid user-defined state, just as "changed" is, and you certainly wouldn't want us overwriting changed files randomly.