I think you could be onto something with Cobb's resolution seeming to be tacked on after Fischers. I do wonder if it's also partly that he's the architect (no pun intended) of his own misfortunes which some of Nolan's other characters aren't really, or they are, but at least they're up-front about it (not that I can blame Cobb for not being upfront about it) and I wonder if that's an issue.