The decision of the court actually makes the situation BETTER for Germans.
Until now the owner of an open wlan could be sentenced for everything that happenend over his network. He was directly responsible for illegal file sharing via his network, regardless of who really did that sharing. He had to pay compensation to companies also, even if it could not be proved that he has done the crime himself. Companies usually got immense compensation for each file.
Same is true when your car is getting into a speed trap and is photographed but the driver cannot be seen clearly. Even if you prove that you did not drive the car you have to pay the fine because it is YOUR car and you are responsible who uses it.
NOW the court says that an owner just has to pay 100 euro at the most if ANY criminal act has happened via his network (because of the nice german word "Stoererhaftung"), but he is not responsible for the criminal act itself and so does not have to pay any compensation to companies.
This means: Open your wlan, do illegal file sharing all the time and if somebody gets you and wants to admonish you, all you have to pay is 100 euro and be more careful the next time.
Now think for yourself if this is better than before. :-)