Note that nobody implements Office Open XML as in the ISO standard.
Microsofts implementation is incompatible to what ISO specified, mainly because in the ISO standardization process, ISO dropped some of the byzantine stuff in OOXML. Microsoft never adjusted its implementation to that, so AFAIK today there is no implementation of the standard in existence.
Which is what is so frustrating about major corporations and their approach to the law. Or rather how the law is enforced.
Small deviations from speed limits are not particularly harmful, but small deviations from the standardisation process here or breaching insider information rules in banks make a mockery of the system. They can pass the infractions off as unavoidable incompetence, but really the system should not except these specious half-truth excuses in these circumstances and should come down much harder, sooner and more often.
Governments often require "standards" in their purchases for very good reasons, like not requiring all citizens to purchase a proprietary solution to interact with them or getting lower prices thanks to competition. If vendors claim to be delivering standards, but aren't really then it's not much different from selling devices or services that don't meet the requirements. Obviously there is a line where incompetence becomes fraud.
I like how Joel explains the necessary reasons why the file formats in question have to be so bad, while tacitly admitting that having a good reason for being bad doesn't make bad code any more useful.
The takeaway for me is that designing, developing and maintaining a full featured office suite is incredibly hard. And standardizing it is even harder. Look at all the teething problems that ODF had.
Microsofts implementation is incompatible to what ISO specified, mainly because in the ISO standardization process, ISO dropped some of the byzantine stuff in OOXML. Microsoft never adjusted its implementation to that, so AFAIK today there is no implementation of the standard in existence.