I also believe that the rumor (not sure if ever confirmed?) was that Rizzo balked at trading Detwiler for Bourn. Who knows how that will look a year from now, but right now, Detwiler is pitching pretty well.
I thought that was a dumb lack-of-move, but a lot of statheads thought Bourn was riding an absurdly high BABIP last year, and Detwiler's been making us look good so far. Bourn's as good as ever, too, though.