Right now it is assumed that a good hitting but not very good throwing catcher makes up for his defensive weakness with his offensive prowess. Do we really know that to be true? And if only a few runs actually were created by the stolen base then perhaps the throwing ability is not that big a deal. There certainly have been a lot of very good hitting catchers who have had long careers without being known as good defensive catchers. So the people running these teams valued the hitting well above the defense.
If Varitek had hit .280 with 25 HRs in each of the past couple of years, but still had the poor CS percentage, I would be willing to bet that few people would be clamoring for him to be replaced.

