I have to say, the bit that made me think the most is where Cat pleads with Walder to spare Robb, making various promises and vows, and Walder snorts and brushes her off. He was right to do so, funny enough, by the terms of honor this world operates on.
The problem with Ned, Cat, and Robb was that, by the lights of Westeros, they all shared a mass delusion: that they were the good guys. It's not just that the Starks had honor. They saw themselves as being the most honorable and pure family who did things "the right way", etc. And because of that they could talk themselves into dishonorable act in the name of the greater good. Robb made a hollow vow to Walder Frey because getting soldiers and taking down the "evil" Lannisters was for the good of the land. The good guys had to win, right?
Robb betrayed Walder because "twoo wove". It was practically stereotypically romantic that the beautiful lady from a faraway land sweeps in and they fall in love and even conceive a child and heir on like their first try. Walder's epic troll with his secret perfect daughter shows he was actually intent on doing Robb an excellent turn by Westeros standards, giving him the best of everything.
Meanwhile, contrast with Jaime Lannister's previous confession about the truth behind his "kingslayer" nickname, where he took down the mad king, saved a city like a big damn hero, but was reviled as an honorless pig of the arrogant and wicked Lannister dynasty.
I guess the final takeaway is that in this story there will be no good guys who are ever recognized and rewarded as such. Things are as grey as can be.
