Building Metro Style Apps is not so easy and the requirements are heavy. The Store is open for every app that meets all the requirements and all of them are described in the Visual Studio 11 local help. When selling an application becomes part of your business model, the requirement list is more than a software certification like “certified for windows x”. It’s not a marketing logo. If your app does not comply, it won’t be on the store. Check also the dependencies. Some applications have to provide both 32 and 64 bit versions. Some need x86, amd64 and arm targeted apps. Whey do many constraints?
The Windows 8 paradigm is provided and built upon native technologies so you have to understand the compilation steps. You can still rely on C#/XAML way to deliver an app but you miss a lot of features. Think about it. Windows 8 is native. WinRT is native. Windows Runtime Library is template library using native C++. Choose well because a lot of things differs from each way. Even if marketing tell that “all languages are first-class citizen”… there is only on first-class language witch is C++. Windows is always powered by C++. If you need to take the market advantage, stay native.