Person B) Why, if it has no additional interop benefit over saving in DOC format?
Persona A) Because we standardized on OOXML format.
Obviously "standardized on" is just restating your original premise in different words.
So once again, why use OOXML? If this is just a pointy headed boss thing then I doubt I can help you much. Companies that standardize on OOXML without a good interoperability reason for it are unlikely to be the kind of companies that roll out open source office suites.