seems to be a good deal of chatter recently about our support for the modified version of Open XML that resulted from the rigorous ratification process. 

The best summary of the story I found is over on Oliver Bell's blog here so I won't retype it here.

I guess people do just expect Microsoft to pull quality code out of a hat these days but it will take some time to bring Office 2007 back in line with the modified standard.  This was always going to be the case.  This should not be interpreted by anyone as any sort of reluctance on our part to do the work, quite to opposite. 

The debate came from this comment Alex Brown made in his post about this effort:

Given Microsoft's proven ability to tinker with the Office XML file format between service packs, I am hoping that MS Office will shortly be brought into line with the 29500 specification, and will stay that way. Indeed, a strong motivation for approving 29500 as an ISO/IEC standard was to discourage Microsoft from this kind of file format rug-pulling stunt in future.

As Chris Capossela said:

We’ve listened to the global community and learned a lot, and we are committed to supporting the Open XML specification that is approved by ISO/IEC in our products.

More commentary from Doug Mahugh on that post from Alex which is a good read.  In his comments he says:

Yes, Max, the day that the vote passed our products didn't automatically start supporting the changes that were made to the spec in recent weeks.  And keep in mind that the final spec isn't even available yet from ISO/IEC.

I'm doubtful that there has ever been a product that has supported a standard as of the day it was ratified, but if that has happened then it would have to be a standard that was not materially improved or modified during the standardization process.  That's not the case here: the standards process improved the IS29500 text, and we're all better off for that in the long run.

and later:

we've not announced any details like that yet but I'll post details when we have them.  One thing to keep in mind is that most users want interop across the widest possible variety of implementations.