Ok, so what if you are a desktop .NET developer (XAML, C# or VB etc.) and web development is something you don’t want to do. Well Windows 8 modern/store apps still use XAML, something that WPF developers will be comfortable with. But as mentioned before, if you want to take your skills to other platforms, you need third party support.
Xamarin is a platform that allows you to write .NET code that will run on iOS and Android. They use the mono framework (a port of .NET to Linux) to enable this magic the happen.
Xamarin also takes an unique approach to cross platform development. It uses a platform specific view layer and the View Model, Model and lower layers (in a MVVM architecture) are reused. So if you need to use Xamarin, you do need knowledge of creating views using XCode (for iOS) or Ecllipse (for Android) using the native code. The VM obviously is impacted by the View itself, but the model and below is all .NET code.
So if you are a .NET desktop developer using WPF/SL or similar you are quite comfortable with MVVM and a lot of your skills will directly transfer to the mobile platforms using Xamarin.