Up to now the role of an operating system has been to create a piece of software which does just about everything for you. A somewhat mothering approach that not only takes responsibility for tying together all your hardware and software, but in bundling applications for everything the average user may need. It is a bloated approach which has seen versions of Windows in particular get ever larger and include everything from media players and web browsers (much to the chagrin of European courts) to unzipping and backup software.
The logic behind this evolution seemed sound: the more you provide the less users need to go to your rivals allowing you to curtail their operations and strengthen your market position - all the while being able to claim you are only trying to help your customers. This is fine until a) you get sued for anti-competitive behaviour and b) the Internet evolves to the extent where it can take over much of this functionality and in doing so relieve hardware of the heavy lifting.
Consequently the threat Microsoft faces isn't so much from rival Windows platforms - its lead is too big, but rather from the changing habits of its customers who find they can perform the majority of their day-to-day computing needs in a web browser. The model isn't perfect - just try convincing heavy Photoshop users or CAD designers that the Cloud can solve their needs - but it is enough for the masses who only require web surfing, email, access to social networks and word processing. The need for a complete Windows platform is never likely to go away, but the risk for Microsoft is it could become niche.
It is this shift which Google's Cloud Computing dependent Chrome OS is counting on, but equally it is key to Apple's iOS which aims to simplify the user experience as it embarks on what appears to be an intentional crash course with Mac OS. It is also significant that tablets are only now beginning to find a mass market appeal after they moved from desktop originated OSes to more intuitive smartphone-based platforms.
The mobility moves we have seen in our analysis of Windows 8 suggest Microsoft is alert to this threat. The risk is it doesn't have the same level of credibility in the mobility space as many of its rivals and continuing to dominate traditional desktop and laptop sectors won't mean much if those sectors do turn out to be on the cusp of radical change.