From a reader comment on the MacBU blog:

Tell me again why it's called 'Open'XML format if even your own company's software can't read it when it comes out?

Well done. The new document format is supposed to be open, ostensibly to allow non-Microsoft products to read the files. Yet it's a complicated enough format that Microsoft's own Mac Business Unit won't have a translator of any sort for the new standard until several months after its release for Windows.

This sort of "open obfuscation" deserves a closer inspection. Kinda like when I tried to figure out what was going on in Furthurnet's code and couldn't make heads nor tails out of parts of it (I eventually got it to work on Mac Classic by mechanically porting its code, not by figuring out what was going on), open doesn't mean easy to understand. This isn't html, folk, and even MS Word's html is pretty complicated to piece apart.

It's a shame Microsoft has poisoned the word "open" like they have. Their stuff might not be much worse than some open source projects, but here I believe it's much closer to being intentional. Certainly MS did nothing to break the impression that "open" meant they were lifting their Word monopoly and allowing 3rd-party competition. Though I can't fault them for trying to make a buck, their "open" standard's double-speak, as shown by the MacBU's trouble creating converters, is despicable.