Nah, the frustrating part is the coaches/trainers can't have an open, frank discussion with you unless your kid gives them express permission.
I agree, this has nothing to do with the kid and everything to do with control of information. Let's face it, information is power, and the coaches want to keep as much of that power to themselves as possible. In this instance, I have no problem with the coaches wanting to control comments regarding injuries. Realistically, no one knows the extent of an injury until often times much later. Think about the number of questions the coaches receive about injuries that they really can't comment on, legally.
To me, the way to control something like that is for the coach to state that he can't comment on it legally. Just as you indicated.
They (coaches) can't control the media. Now, to me, "journalists" should have enough integrity to not disclose things without attribution (I think that's the right phrase). Unfortunately, the "journalism" field is dead.