Cogman was probably thinking of the markup, which was certainly the major conceptual change in WPF, but yeah there is a lot more to it. XAML is a declarative way to create control trees, just as in ASP.NET, and as was mentioned previously you don't need to use XAML at all. So really it's about a new framework of classes for compositing UI elements and driving their behavior, and the underlying technologies that enable it (the DWM on DirectX). As for learning it, I would just dive in and start making something.