As previously reported here, a number of German universities are trying to rescind the doctorates that have been granted to persons who either bribed their way to the title, used ghostwriters, or just plain made up their data.
Spiegel Online reports that this is a nice idea, but hard to do. German universities are actually an arm of the government, the professors are civil servants. And there are lots and lots of Prussian-style laws (as well as a Nazi law fron 1939 that was used to take doctorates from Jewish scientists, "Gesetz über die Führung akademische Grade") regulating how you go about doing this - or rather, not.
The upshot is, that it is not easy to rescind doctorates, and there are lots of lawyers eager to help the poor plagiarists and fancy fraudsters keep their titles engraven in bronze on their front doors.