Developers Developers Developers
MSFT is too late to get all the cool kids on windows tablets - even Balmer's kids aren't clamoring for a Win8 phone to play minesweeper.
So most of these devices, like all win-ce are going to be used commercially and industrially. That's one place they can beat Apple and Android.
Try getting an expensive or restricted commercial app on appstore. Even if you are happy about giving Apple a 40% cut, or finding that only customers in the US could download it, having no way to attach an XYZ brand bar code reader or portable printer, then having your FDA approved medical note taking app rejected because there is no way to follow a patient on twitter or some other Apple style mandate.
Android is even better, if you don't mind coding for 57 different varieties and having an appstore that guarantees your app is pirated onto the chinese app store as soon as it's uploaded.