It's a pretty good example of why MS cannot be allowed to control a supposedly open standard for office file formats - witness the dubious shenanigans as MS attempts to have OOXML certified as a standard. It's just not in MS' nature to be open about proprietary formats, especially where these are key to the market dominance of their premier product.
Fortunately, we have an alternative: OpenOffice.org - a full-featured suite of office applications, available for Windows, Mac, and Linux. It supports the genuinely open standard, open document, and furthermore has the capacity to deal with the older MS Office file formats that MS don't want you to work with.
More on why MS OOXML is a bad idea, dubious ISO committee work, and other stories (from an anti-OOXML point of view.
On the other hand, my work PC has MS Office 2003, with service pack 3, and it can open word files I created back in 1999, which according to "properties" are Word 97-2003 format (whatever that is). So I don't know how serious a problem this might be. Upon trying to open an old Word file created in 1993, I get an error message.