The problem is that there's a whole US generation not being brought up in a PC household. You don't think kids of today are gonna make purchasing decisions of tomorrow? That companies are going to be able to sustain a PC-only environment in the face of the fact that the majority of college students are using Mac? That businesses across the board are adopting "BYOD"?
This is what should terrify MSFT - this is absolutely devastating. This is why they have XBox. This is why they attempted the Zune. This is why they have a tablet.
Yes, the business environment is MS' bread-and-butter, but it's going to suffer catastrophic hits over the next 5-10 years as the "Anything-but-Windows" generation grows up. You seriously think that companies will be able to maintain their MS hegemony when the majority of new employees have grown up with a Mac, iOS, and/or Android?
Make no mistake - this is huge, and what will break Microsoft's back. A diversified IT client base breaks Microsoft's stranglehold. You pay a fortune (a definite price premium) for Exchange, Office, SQL Server, Sharepoint, Windows Server, etc. because it gives you labor/cost savings in an all-PC environment.
Once you throw iOS, Mac, Android, etc. devices into the mix, you no longer have that advantages. If I was a CIO or CTO and my business users were complaining that IT is too restrictive, that it's impacting hiring and employee retention - there's no way that a "MS-only" policy is going to stand. If you're a startup or other small/medium sized business - why wouldn't you switch to Google Apps for Mail? Oh, and it includes a lot of other things, too (groups, "office-lite" collaboration; oh and a Chromebook that "just works" within this environment).
Not that MS won't still be a big player in businesses but a lot of the "demand" for MS business apps are propped up by economies of a homogenous environment. Once that starts to unravel, there's no stopping it.
ref
http://macdailynews.com/2012/06/06/gartner-apple-macs-invadi...
http://plzkthxbai.com/blog/2009/09/24/nearly-58-of-college-s...
http://daringfireball.net/linked/2010/08/08/mac-share-colleg...
http://tech.fortune.cnn.com/2010/08/07/big-macs-on-campus/