Why would you need such a thing?
There are many subtle differences with Microsoft's installer, getting apparently the same software version from different vendors can result in otherwise legitimate product keys not being accepted. For example, OEM licences do not work with the correct version downloads from Microsoft's own web site.
Microsoft's application licensing is far more troublesome and complex than their operating system licensing, and that's dad enough.
Open Office FTW!
Incidentally, I now see that Office 2010 has now fully adopted the Open Document format that has been used by Open Office and many other open source office software.