Also I think Payton puts a lot of emphasis on training camp. I think he has an open competition there and once you are a starter, you stay a starter until injury or FA dictates otherwise.
That theory (if indeed it is his mindset) is good in the sense that you are not going to have a knee jerk reaction to poor play and you make guys earn their spot when they should, training camp, but you are also less ope to change if a player is preforming poorly i.e. David.