You do know it's possible to embed binary formats in XML, right?
Yes, I do. I also know that the document as such, in OOXML is not binary encoded. The article you refer to gives a clue, it appears that Microsoft embeds printer settings in binary format in the XML. This may or may not be a problem, depending. OOXML does not as your referenced article alludes to, use the binary format to specify the document size. The paper size in OOXML is defined thusly: <w:pgSz w:w="12240" w:h="15840" />
So, yes, XML can contain binary data, and yes, OOXML documents appear to some times contain binary data related to printer setup, but no, that binary data does not appear to have any impact on your ability to parse said OOXML. So, going back to the post that I replied to, no, OOXML is not opaque binary data, it is perfectly readable and parsable XML. Are there other problems with OOXML, yes, I don't think the referenced conformance clause is a problem, yes, legalistically it can be, but in practical realities, no, it is not. Non-covered implementation-defined content may be a problem, but it is currently not.
Are there problems with OOXML? Absolutely. Is it a binary opaque blob (which is what I commented on) no, it is not.