David Roundy [off-list ref] wrote:
You're right. I figured I must be overlooking something obvious, and
that was it. What surprised me was that -p implies -r, which is not
documented. Since the -p output was recursive, I incorrectly presumed
that this was the default.
I suppose that's because you can't really display the diff for a
directory in any meaningful way other than recursing.
Jan