Corporate PCs: Underpowered for Vista. Overpowered for Writely?

I'm not singling out Google's Writely because I think it has a better shot against Microsoft's Office than any other Web-based contender.  I just needed to pick one (of the many Web-based offerings) to make a point that Microsoft could be seriously shooting itself in the foot if what Gartner says is true.  According to InformationWeek's Antone Gonsalves (via Bob Sutor's blog):

About half of corporate PCs aren't equipped to run all the features of Windows Vista, and companies should gradually deploy the upcoming operating system on new computers, rather than take the more costly alternative of upgrading older ones, Gartner said last week.

The story goes on to cite Gartner analyst Mike Silver who basically said that from a shock to the coporate digital infrastructure perspective, Vista will be more like upgrading to Windows 2000 [from Windows 98 and NT I'm assuming] than upgrading to Windows XP [from Windows 2000, I'm assuming]. 

What struck me as being sort of odd is that there's no mention  (either by the InfoWeek reporter or the Gartner analyst) about whether it's finally time for corporate America to rethink the upgrade treadmill by going back to the future.  After all, there are plenty of older PCs that have more than enough horsepower to run browser-based office offerings like Writely that are starting to come of age.  So, how much has corporate America paid for hardware over the last three or four versions of Windows just to make sure it can continue to run its software?  I don't know.  But now seems like a good time to ask whether or not more is actually less.