Wow! I was in a triad that deteriorated quickly due to insecurity of the wife. Her husband, who I also loved like my own, also deferred to her, but in our case it was in an effort to try and reassure that eventually failed.
However, this behavior that you are describing sounds very similar. Could it be that she was initially insecure and that this deference became a habit?
Has it grown worse over the time you've been with them or remained about the same?
Or is it possible that this deference was how their relationship was before you entered the picture and so they are behaving as they always have? In which case they probably just regard it as normal. If this is the case, then I agree, their interaction should have been modified somewhat to accommodate you better.
In any case, it sounds like the issue needs to be discussed.