The C is not a popularity contest and the C should not automatically go to the best player on the team points-wise.
The captain is the in-between with the refs and the coaching staff. Language barriers (Kovalchuk is not a native English speaker) do not help with this.
The captain has to be a leader on the ice and in the locker room. We don't see Salvador in the locker room but the coaches do--that should tell you something.
The captain has experience, leadership qualities, proven himself under stressful situations and is a team player. Salvador's career could have been over two years ago but he came back stronger and better than at any point in his career.
I laughed when Crosby was named captain of the Penguins at such a young age. If I was a 35 year old NHL veteran, I wouldn't have taken him seriously, even if he put up 200 points a season.
The captain also can't suck!