Carlo Piana, lawyer and legal counsel of FSF, comments on the lack of reasons for OOXML to exist. He also points out that the standardisation process is led by the need to be compliant with one vendor's product:
Thence — for instance — the need to preserve the 1900-is-a-leap-year bug, blatantly ignoring that a) we have been in a Gregorian calendar, and not in a Julian Calendar long since and b) that there is an ISO standard (8601) on Representation of dates that cannot be disregarded. In other words, it is the implementation that leads the standard, not the standard that guides the implementation, and this is plainly unacceptable.
I could be biased in my opinion, but a standard that ignores all the standards and even the rules of standard-making processes, should not be an International Standard.