Looking at the amount of solder remaining on the pins in your picture, it would appear that your iron is not hot enough, or you are not waiting long enough for all the solder to melt before applying suction with your desoldering iron.
I use a Pace desoldering iron and when done properly you can vacuum off just about every spec of solder. I've had IC's and header pin rows literally fall out into my hand with no external force. Pace irons are expensive but so worth it if you are going to be doing board rework.
As for the oxidized copper left behind, I use Zep toilet bowl cleaner and they shine right up and the solder sticks like it's supposed to. There's another thread on Zep toilet bowl cleaner here on Pinside as well.