In every file there is a section of "code" known as the creator code. If you create a file in word, the creator code will belong to word. If you create a file in pages, the creator code will belong to pages.
In Leopard, the OS used to look at this creator code and open with the relevant application. That's why some JPEG files would open with preview, some with Photoshop, etc etc, even though they are the same file type.
Snow Leopard now ignores this creator code and opens documents with the default handler for that file type. So all docx will open in Pages, if that is your default, regardless of what application created them.
I hope that makes sense?
Basically Snow Leopard hasn't made iWork read office files, but it has stopped the computer opening the file with the application that created it.
Tom