Now is not the time...
...for this argument between OpenXML and ODF to arise. The time for this exchange to occur was back when the ODF standard was being proposed and in review.
Very simply put, if Microsoft had a reasonable set of extensions that Microsoft felt were needed to provide enhanced functionality to XML, they *SHOULD* have proposed them for inclusion in the initial draft standard. This would provide Microsoft with the extensions required for Office, and maintained a single standard for all users.
Users don't buy software on the basis of underlying standards, this much is absolutely true. The distinguishing features of the user interface and integration with other applications are the key determinants for acceptance of *ANY* software in the real marketplace.
Microsoft *WOULD HAVE* continued to dominate the office tools marketplace even with ODF as their standard for document storage. Period. No, make that *WILL* dominate, regardless of the outcome of this standards argument.
HAVING SAID all the above, Occam's Razor provides some logical insights into the standards battle today:
Microsoft COMPLETELY FAILED to grasp the importance of XML as a fundamental technology;
Microsoft RECOGNIZED AN IMPENDING BUSINESS PROBLEM in the sales of Office, either CAUSED by XML or other Microsoft marketing/sales/design/management issues.
There is also the fundamental difference between a corporation an a standards organization. A BUSINESS exists TO MAKE MONEY for its STAKEHOLDERS. A STANDARDS BODY exists to SAVE MONEY for its STAKEHOLDERS. These goals are usually congruent, especially if the stakeholders are of relatively equal stature in the standards organization, but are often at odds when there is a split among the standards body members about the BUSINESS ADVANTAGE that a particular standard conveys. (See OSF-1 from POSIX as an example of the latter.)
Microsoft Office is a KEY REVENUE STREAM for Microsoft, and one that has been troubled time and again by inter-interoperability and cost issues. (How many organizations still use Office97 formats as their "standard" for document production due to incompatibilities in newer Office versions?) Microsoft has already publicly discussed sales issues with Office 2007, and Vista has taken far more resources to launch than was anticipated, making the adoption of Office 2007 a competitor for sales, marketing, development and maintenance resources.
My conclusion is that Microsoft has correctly identified ODF as a threat to its hegemony in the office suite market. It is a threat of the same form as .pdf, another "standard" that caught Microsoft by surprise, driven by the needs of the market rather than the need of Microsoft. (Microsoft still does not provide native support for .pdf files in Windows...isn't that a bit odd these days?)
Microsoft, in my opinion, feels that ODF threatens the uptake of Office 2007 significantly. Microsoft also recognizes that it made a strategic error in not dealing with XML decisively early on.
OpenXML is *NOT* and attempt by Microsoft to defeat ODF or XML at this late time; rather, it is simply a "stalking horse" to *DELAY* the uptake of ODF until such a time as Office 2007 is back on track to replace existing Office as the de-facto productivity tool. At that point, I expect Microsoft to jump up and shout "JUST KIDDING!" and "embrace" the "standard".
Meanwhile, if OpenXML becomes a competitive standard, well, all the better for accelerating the uptake of Office 2007.