Nah, there's lots of other ways to get people to slow down. I mean, speed bumps/humps are
one way, and they have their uses, but you can also add trees (yes, it's a psychological thing), narrow the road (e.g. add bike lanes or extend sidewalks), make the road less straight, add roundabouts that people can't blow through, add chicanes at some points (I've seen this in the bay area), add diverters that discourage car through-traffic, etc. Lots of options.
The most obvious difference I see between Germany and the US is that the roads are just way wider in the US. That makes drivers feel like they can go faster, so they do go faster, thus making them less safe. You don't really need to enforce tight speed limits in neighborhood streets where I live in Munich, they're so narrow that it's very obvious that you cannot go fast.