I think it's based on the (fahrt fahrt fahrt auf den) Autobahn. Now, I'm not german so I could be wrong, but here's what wikipedia says regarding speed limits on the autobahn:

Much of the system has no speed limit for some classes of vehicles.[1] However, limits are posted and enforced in areas that are urbanised, substandard, accident-prone, or under construction. On speed-unrestricted stretches, an advisory speed limit (Richtgeschwindigkeit) of 130 kilometres per hour (81 mph) applies.[2] While driving faster is not illegal in the absence of a speed limit, it can cause an increased liability in the case of a collision (which mandatory auto insurance has to cover); courts have ruled that an "ideal driver" who is exempt from absolute liability for "inevitable" tort under the law would not exceed Richtgeschwindigkeit.

So, it certainly seems there is a basis for the jokes, even if they aren't 100% historically accurate.