I'm wondering this. The example code I've looked at has it as a resource, which can be any type of object. What is it about this class that requires visual attributes?
It doesn't need any of the visual properties but it was done so one could define an instance within xaml and it would have access to the DataContext should you want to bind some of its properties and more importantly so that controls in the visual tree could get a reference to the object (e.g. through an ElementName binding) such as when you set the CalculationManager property of multiple controls that will participate in the calculation network.