This is interesting, so I've been poking about in the Win8 SDKs to try to find the information you're looking for.
1. There's an explicit setting when you install Win8 regarding whether apps are allowed to send usage metrics to Microsoft. This data is collated under your Microsoft account provided you choose to allow it. If you choose not to allow it, no data is gathered.
2. The DNT:1 header sent by Internet Explorer 10 does not persist into apps. However, each app makes HTTP calls in its own session. You could in theory have an unlimited number of browser sessions open with an unlimited number of applications and there is no means of cross-referencing between them (unless done explicitly through Contracts, where an app sends a 1-way message to IE about, for example, what URL to open).
3. There isn't a Bing Maps app (that I can find). However, the SDK allows developers to build mapping functionality into WinRT Metro apps. Apps can only communicate with each other through Contracts (see #2). This does create the potential for an unscrupulous app-maker to implement app-to-app tracking, but only for apps which they themselves developed. None of the MS apps available implement this (and it's easy to tell because the source code for all the "majors" is provided in the SDK as example code).
The summary is that you could probably track users via apps if you could make them use many of your apps all at the same time but MS don't (and publicly say that they don't). You could not track users between apps and IE10 or (and because this would imply dropping to Desktop mode, I can be certain) between apps and any other browser.
If you wish to indulge in tinfoil-hattery, you could theorize that MS track everything via Microsoft account (if you use one) and that the released source of their apps is not the production source of their apps but that's delving deep into "they'm watchin me with rays, them and their big weasel" territory.
It's in Microsoft's best interests to appear to be the "The Good Guy" to their customers. Advertisers are not their customers, users are. Therefore, the logical take-home is that MS is unlikely to fuck over their customers.
You could say the same about Google but in that case, the advertisers are their customers while the users are not.