It appears that the problem with the Microsoft Office Setup Assistant app not updating has something to do with product registration (go figure...). I am still investigating:

Cause:  An error in the Microsoft product registration system caused the system to reject some valid Office 2008 for Mac product ID numbers.
Solution:  Try registering again.
Microsoft has corrected the error that prevented the Microsoft product registration system from accepting some valid Office 2008 product ID numbers. Product registration is not required to use Office 2008 for Mac, and your product will work correctly regardless of registration. All customers who were previously unable to register are encouraged to try again. To access the online registration system, on the Excel menu, click Online Registration.