if you'd argued that the Docx format is unecessarily verbose, well that's a possibility (Although the problem is that MS are dealing with 30 years of legacy here, it's not a simple task. One of Word's better achievements is that I can generally open 20+ year old documents and they'll render just like they did back when they were created)

but to say that .docx is a binary file format, nope, it's a zipped text file format. If you parse docx you unzip and use an XML parser, you don't use a binary parser.

.doc was a binary format, but that's not been a default file format for Word in the last 15 years.