My mind went blank after reading the following:
For instance, the underlying attached event Mouse.MouseDown can more easily be handled on any given UIElement by using MouseDown on that UIElement rather than dealing with attached event syntax either in XAML or code. The attached event serves a purpose in the architecture because it allows for future expansion of input devices. The hypothetical device would only need to raise Mouse.MouseDown in order to simulate mouse input, and would not need to derive from Mouse to do so. However, this scenario involves code handling of the events, and XAML handling of the attached event is not relevant to this scenario.
Anyone care to explain this one?