I was under the impression their hand was forced. I vaguely recall various nation governments insisting on open standards or they would no longer use Office.

The OpenOffice formats were going through standardization and Microsoft quickly bought their way through the standards process (this part I remember). There was a lot of complaining of how they exploited the particular standards' body. They bought seats, that then sat vacant after they got their standard pushed through, and couldn't meet quorums on other standards being voted on.

There were also many complaints about the Microsoft standards themselves. Particularly, that you couldn't implement support for the documents based solely on their standard.

Correct me if I'm wrong.