The design of the Windows Runtime, combined with slick C# language support, could lead one to think, “Threading model? I didn’t realize universal apps had a threading model.” In C#, you get to enjoy the benefits of writing an app that largely feels single-threaded, but has all the power of asynchronous code (and a number of parallelism mechanisms employed internally by the Windows Runtime).
Supporting multiple windows within a single app is one area where the code you write can become awkward, but the model of having each window run on a separate UI thread maximizes an app’s responsiveness.
Finally, the features enabled by Frame and Page support the navigation paradigm common for universal apps. Almost all apps use multiple pages.