A penis is not an a gun you accidentally fire into a woman when you're not careful. Robb was pretty stupid in the books and the TV series, end of. It's true there's more forethought in him going after Talisa, but then, is this considerably older Robb the kind of man who'd randomly screw a girl and then decide he needs to marry her? I do wonder if part of the reason the plot was changed was to accomodate that he's quite obviously not sixteen.
But then, generally speaking, Robb is meant to be a character who has a natural gift for war but less than ideal judgement in political matters, leaving him as a man who both never lost a battle and also lost everything. The Talisa plot fits perfectly the man who'd innocently deliver Theon into the hands of his old family.
Not that I'm that wild about the Talisa story. Assuming she's part of that whole Tywin Lannister plan hinted in the books, how does it work? If both Robb and Tyrion end up betrayed by their beautiful foreign women 'cause Lord Tywin is pulling the strings it'll feel a little redundant.
So Arya's going to leave Westeros before the Red Wedding? Unless I'm misremembering, that's an arguably-important change for her motivation to go...
She's not. Jaqen offered to take her to Braavos, but she said she wants to find her sisters and brothers and mother and the rest of it. I'm assuming that means the show will just set her on the course towards Catelyn.