vtk mfc examples: vtkMDI vs Win32SampleMFC

I am new for vtk and trying to learn it through some examples. I saw there are two vtk examples (vtkMDI and Win32SampleMFC) and they seem for exact same functions, but quite different designs. The Win32SampleMFC with two extra view classes and one extra doc class, comparing to vtkMDI. Can someone explain why?

Thanks a lot.