Looking into it today, it seems what a patch looks like depends on the tool. Git by default (using a command like git format-patch) adds a From: header value that contains the original author. Mercurial (using a command like hg export) includes the original author, but it shows up in commented lines.
However, looking at the devguide (http://docs.python.org/devguide/patch.html), they tell you to run hg diff, which creates a barebones patch file with no author metadata.
Does anyone know if hg has a similar author vs committer distinction? If so, perhaps the tool is displaying committers by default?