I suspect some of the apparent muddle of grading Moodle discussions stems from Moodle's social constructionist pedagogy, which posits that educators are supposed to care more about building knowledge through discussion (or "negotiation") than they are about transactional grading, which is something D2L really excels at.
Yeah, I think the forum ratings system was really meant for students to rate each other. It was not designed for teachers to apply a rubric to the post - which is what D2L allows.