I have been wandering about the Westerlings and their involvement in the plot against Robb. It seems pretty obvious from the fact that they were not only pardoned by Tywin Lannister but that Jeyne's uncle was given Castamere, that they were hand-in-glove with the Lannisters/ Boltons and Freys in the plot against Robb also the fact that Jeyne's mother was giving her a contraceptive or tansy every morning that they meant to make sure that there was no chance that Jeyne would ever get pregnant.
Well, we shall see.
But I think it is a mistake to generalize about "the Westerlings," just as it would be to generalize about "the Lannisters." Members of the same family have very different characters, desires, and ways of looking at the world... and there are secrets within families as well.