Unfortunately, Windows 8 tablets and the hypothetical Windows 8 phone that turns into a full desktop when you hook it into a monitor will both run on the ARM architecture. These are not binary compatible with existing Windows executables.[1] This means that any advantage that Windows has in quantity of applications does not translate to new types of devices. When it comes to phones and tablets, unless Windows gets the market share first, there will not be (m)any "killer apps" for the new platform that aren't first-party Microsoft apps. I'm not sure that Microsoft Office is important enough on mobile devices to convince everyone to switch.
The largest advantage that Windows traditionally had (almost all the apps are written for it) is gone as soon as you make the switch to ARM.[1]
[1] https://en.wikipedia.org/wiki/Windows_8#Software_compatibili...