Catcher "ERA" has been studied time and time again. Really, there is no reason to believe one catcher will work better with any one pitcher.
If you have small ample sizes it can look like that for a time. But, for example, was Benji so great because Lincecum was so good with him and not Posey? Or is Lincecum simply not the same pitcher he is today that he was in 08 and 09.. I think most people would say he's just not the same pitcher.