As far as I'm concerned all the blame belongs to Bochy, but as a GM there must be a way to convince him to play Nady. If I was GM I'd trade anybody that Bochy put in Nady's place. You want to play games Bochy? You want to play games? We can play games!
In my mind there was absolutely no reason why Nady shouldn't have had first base all to himself after Nevin left. Why give the job to utility / bench players like Fick and Sweeney? They did nothing special out there. Bochy must have been the only person in San Diego that didn't see that Nady was one of his best players.
Oh also, I don't buy the whole "matchups" reason that Bochy gives for not playing Nady. There was something else, there had to be something else. You don't sit one of your best players for the entire year because of matchups when you run out Klesko out there day after day when he obviously sucks. I'd love to know the real reason, it's got to be some amazing story.