However I'll admit i don't know the Specifications in the USA, so tell me if I'm mistaken.
We have:
30 km/h in areas with lot of pedestrian traffic/ school zones
50 km/h anywhere else in a city/town
70 km/h on designated feeder roads inside cities
100 km/h outside cities/towns
120 km/h Autobahn

I have never seen any like that in Germany.

But I'd hazard a guess that in Europe Speed limits are a lot less arbitrary. Most of the time you can already guess it just by the type of road you are on.
And I'd say the same for the Cameras (eg. school zone, high speed feeder road entering town, etc)