regarding "git status"

In the manpage for git-status
(http://www.kernel.org/pub/software/scm/git/docs/git-status.html) it says:

"Displays paths that have differences between the index file and the current
HEAD commit"

but how could something be added to the index and not be different from the
current HEAD commit? shouldnt this sentence say: "displays paths that have been
added to the index"