Opera's Wium Lie puts it like this:
In this conflict, ISO must answer a difficult question: is there room for both ODF and OOXML inside ISO? I'm not a fan of either format, but ISO should be concerned about the closeness of the two formats. They are similar in function, solving the same problems and using XML as the syntactic foundation.
A matter of principle: coke or pepsi?
Further, the letter claims that "ODF is closely tied to OpenOffice and related products" (bad!) while OOXML "reflects the rich set of capabilities in Office 2007" (good!). A more even-handed sentence might read: ODF is an XML-based dump of the internal data structures of OpenOffice, while OOXML is an XML-based dump of the internal data structures of Microsoft Office.