Sales of Office and Server OS offerings by MS are double the sales of Windows. Although MS does target home users, corporate and small to medium businesses are where the profits are for MS. I think we'll see MS clean up Windows 8 as time goes on here so that it is much more palatable for corporate users.
And let's also not forget embedded sales. We will see an explosion of tablet use over the next few years in corporate settings. By being able to deliver a mobile OS on ARM, utilizing existing development tools is a huge advantage for MS. Want to embed iOS on a tablet? Nope, Apple doesn't license it's OS. So what alternative do you have? Android? Sure, it's viable and has the momentum right now but MS can beat it with a solid offering given the huge existing developer base.