WIndows 8 tablet success at the expense of loss in Desktop market share?
Here's a an idea about Microsoft's current strategy. Microsoft and whole industry believes that touch input based hardware and software is the future. Microsoft is betting on this big time with windows 8. We all know that in order to be successful in today's tablet/smartphone market where Apple and Google are clearly dominant players (Google to a lesser extent), a developed ecosystem is very important. This is the reason Nokia went windows phone. This is the reason RIM is unlikely to succeed with BB10. And this is the reason Android is a failure in tablet market.
Here's what I think. Microsoft knows all this very well and that's why they decided to put metro on desktop. We don't know whether Windows 8 tablets will be successful or not yet. We don't know how many of them will be sold to consumers. So there's little incentive for developers to target that audience just yet. But what we do know is that Windows 8 based PCs will be sold in hundreds of millions. And developers will want to tap that market. No wait. They will HAVE to develop for Windows 8 desktop in metro as is evidenced by the fact that BIG players like Mozilla, Google, Netflix etc. are already working on their metro apps for Windows 8. Once metro desktop apps have been developed, there's little reason not to port them on Windows RT (and similarly WP8). By putting metro on desktop, Microsoft has essentially made sure that no matter what there will be apps (and an ecosystem) for windows 8. Within an year, you can expect to have at least 100,000 metro apps in marketplace. This will result in a better app ecosystem for Windows RT and subsequently WP8.
To sum this up, Microsoft might lose some desktop customers in the short run (new ones will definitely be buying Win 8 machines. It's the current users that might not upgrade) but in the long run, Microsoft has ensured there'll be more than enough incentive for customers to buy into the Windows ecosystem.