There is nothing wrong with a law student including on a resume a reference to a law review Note or Comment he or she wrote. When I was involved in law student hiring I regularly saw those, and sometimes even went back and read some of the published material cited by students I was scheduled to interview.
The significance of this in Obama's case is that he has never taken credit, so far as I know, for anything published in the Harvard Law Review. This means either (a) he never wrote anything that was published, or (b) the stuff he wrote and got published is so bad or so inconsequential that he won't take credit for it. Frankly, either (a) or (b) is highly unusual for someone chosen as President of the Harvard Law Review. As I said, it screams "Affirmative Action Baby."