Never saw that, but yeah, I was thinking about this too. Approval is between Blackwall and the other character:
King Alistair: Blackwall would probably see his rise to King as a dereliction of his duty. Little respect, really. -10 approval
Loghain: Depends. Did he make the Ultimate Sacrifice? If so, Blackwall approves +5. If not, -15 approval for not letting the Orlesian Wardens into Ferelden. Hell, he might have even TALKED to Loghain, because Loghain would be at Montsimmard.
Anders: -20 approval for desertion and his acts of violence.
Oghren: +10 approval for joining the Wardens and not leaving
Nathaniel: +10 for joining and not leaving
Sigrun: +30 for being a Warden and Legion of the Dead
Velanna: -10 approval. Only joined the Wardens for her sister, wanting to side with the Architect.
Carver: +5 approval. Good Warden, just needs to shut up about his brother.
Bethany: Neutral. She hates being a Warden, but Blackwall probably would feel bad for her, feeling that this life isn't for everyone.
Warden: Hard to say, really. It all depends on what choices the PC makes. Blackwall probably would largely dislike my character, because she married Alistair to be Queen, did the Dark Ritual, and is also strictly anti-Orlesian (Leliana being one of the few exceptions).