This is because the new docx file format is completely different from the
old binary file format.

In fact, the docx format is a set of XML files archived together in a zip
file with the filename extension changed. if you change the extension from
docx to zip, you can open the file with Winzip and have a peek inside. I'm
sure you'll be able to work out which XML file in there contains the
document properties.

There are enough zip/unzip and XML parsing utilities around, so I'm sure it
won't be all that long before somebody cobbles them together and builds a
property reader for docx files.