My initial thought is consistent with the above, but then I think about my having a feeling that Fred Jackson and Stevie Johnson had looked so good in preseason and I wondered how come they weren't being given a shot - and once they got a shot, they did pretty well. Sometimes I wonder if there's a bias on the part of the coaches to favor one player over another....which happens in all professions to some extent.
Maybe it's different with QBs, because there is so much time and preparation that the coaches feel it's too much of a waste of the time they invested in Fitz to pull him for Brohm, just to see how he does? And when your job and reputation are on the line, it's a lot harder to make a change "just to see how he does".
I know there are some former pro players on here, and I'd enjoy hearing about their experiences with coaches who held back guys with potential and some of the reasons for doing so (as the former players perceived them).
Cue Die Hard and Another Point of View.....