iCloud documents only work with iCloud enabled apps. But right there on Apple's page it says this:
iCloud makes it easy to move Pages, Keynote, and Numbers documents between your computer and your iOS devices. Just sign in to icloud.com/iwork in any modern web browser, and all your iWork for iOS documents will be there complete with your most recent edits. Click a document to download it in iWork 09, Microsoft Office, or PDF format. You can also drag and drop any iWork 09 or Microsoft Office document from your computer into one of the the iWork apps on icloud.com, and it automatically appears on all your iOS devices, ready for you to review, edit, or present.
So will Office for Windows be getting iCloud integration? Or is there a possibility that iWork will be released for Windows?