Much of the talk about the immenent death of Microsoft Windows is mostly based on sales figures for all end-user devices and relative numbers of page reads by different browsers and operating systems. If Information Technology's responsibilities were based on the number of end-user devices sold and on browser page reads, this would be interesting information.
IT's responsibilities, though, have a lot more to do with applications business users rely on to get work done. When you look in this direction, you get a very different bead on things. Let's check out infrastructure first -- in particular, the server OS, DBMS, app server, Web server, development kit, email, and content/document management solution. While IT has choices for all of these, Microsoft doesn't just continue to matter here; rather, it's probably the most innovative force in the industry in this space right now -- except in its ability to explain itself. The infrastructure story for Microsoft is excellent products coupled with incoherent storytelling.
Then there's the end-user computing environment (what's usually mislabeled the "client"). What a lot of analysts miss is quite simple and basic: Microsoft Office file formats are the industry de facto standard, and no amount of de jure standards setting will change that any time soon. Thus, any business that has to exchange documents with other companies has to use Microsoft Office, because the best any competitor can say is that its product can read and write Microsoft Office files.
That isn't the same thing as rendering them properly, and the fact of the matter is, no matter which Office competitor you use, it will scramble Word documents that do any serious formatting at all. As for PowerPoint, you have no idea just how bizarre the results can be until you try running a PowerPoint animation in a competitor's piece of software.
Every version of Windows Mobile so far has been at least one step behind the industry, and there's no hint yet that Microsoft has the ability to leapfrog its competition in the mobile arena. It's natural to figure Microsoft's presence in mobile computing is and will be limited to laptops, which will remain the portable devices of choice for those who plan to do serious work that requires a keyboard for quite a while.
Bottom-line: The increased importance of other platforms represents an expansion of what IT will be responsible for, not a substitution. Windows and Microsoft will be important for a number of years yet -- but so will other platforms and players..