^Well said. That song was a great way to cap the episode and was an extremely moving moment. I've always thought of Kang, Kor, and Koloth as the Klingon equivalent of Kirk, Spock, and McCoy. To see the final member of their trio sacrifice himself for his crew always leaves me choked up when I watch the episode.
As far as Martok not singing, I think he was trying to avoid hogging the moment and wanted his crew- who treated Kor better than he did- to have a chance to say goodbye to their comrade.