Exactly what my teacher wanted, I think

So you may remember my blog about my Sociology paper, or "memo" as my professor called it.  If not, go back and read my blog post Can't escape the BS. 

Well, I got my paper back, and I received full credit for the assignment.  So, what did I do right?  I honestly don't know.  The paper was e-mailed back with no comments whatsoever--no "good point" or "great job tying this back to ..." or "I'm not sure about this..."--nothing at all to help me understand what I should continue to do as a writer to keep receiving perfect grades on writing assignments.  The only part that was contributed to my paper by my professor was the grade: 2.5/2.5.

This really made me think about how important feedback is to writers, especially when the work is going to be (or has been) evaluated.  If a professor were to give me a C on an assignment, I'm sure he/she would have some form of written commentary on what I did wrong or what I could do better.  However, I find it ironic that some professors do not feel the same inclination to comment on the positive aspects of written assignments, especially when assigning perfect scores.  What is it about my writing that deserved all of the points possible?  Is there a certain technique or mode preferred for writing in this particular course?  If so, how will I ever know?  I may never...not without comments...