I would bet that open document standards are as much of a thread (if not bigger) to Microsoft's bottom line than open source software. You're right that Microsoft has relied for years on "planned obsolescence" of their file formats, and that has forced upgrade of Office. Really, when was the last time that anyone needed to upgrade Office because of new features? But can't open a .doc file? Oooops, time to upgrade!
Having used OOo as my main office suite for a bit over a year now, I can honestly say that there are only a couple of features that I miss. However, if people could move to an open document format, that would solve a boatload of problems for me. And I bet that is the case for a bunch of other users as well.