Sue's question is one I've been asked by my own managers and I think it's valid. We made the decision to focus on the exceptions, which gives us more time to focus on items where it's gone badly wrong. This is usually triggered by users or colleagues failing to find something of it being so poorly described as to be useless. But I think suppliers should work together on ensuring that they maintain and promote the 'proper' application of standards, as this would eliminate many of the exceptions in the first place.
Just read Galen's & Nick's post both of which I broadly agree with. Galen is right to bring up the issue of 'other agencies', at the risk of going off on a tangent it is our reliance on MARC, a format only libraries use, that causes many of our problems.