In a 2005 article at eWeek entitled "Microsoft Opens Office File Formats," Alan Yates, the General Manager of Microsoft's Information Worker Strategy, said open file formats would ensure that customers would "not be reliant on one product or one version of a previous product from the past in order to open up those documents."
And spokesman Jason Matusow, of MS shared source fame, is quoted in ComputerWorld thusly: "...we will support interoperability with ODF documents as they start to appear and will not oppose its standardization or use by any organization. The richness of competitive choices in the market is good for our customers and for the industry as a whole."
Perhaps Microsoft is feeling insecure about its chances of having its own XML file format approved as an ISO standard, since lawmakers in Texas especially seem to be leaning toward ODF, writing that the file format must be "controlled by an open industry organization with a well-defined inclusive process for evolution of the standard." Maybe what Yates and Matusow really meant is that open file formats are good (for Microsoft) only if they're issued and controlled by Microsoft.