More likely it's the lower number of driving-hours per-person. The longer you drive, the greater the odds that something can go wrong. Germany, like most of Europe, has dense old urban cities and good transit infrastructure compared to American suburban sprawl. That means the average German doesn't spend as much time behind the wheel, if at all.
I wouldn't be surprised if Germany is substantially more dangerous per-driving-kilometer than the USA, but with far fewer driving-kms per person.
Also, remember that in many locations the "speed limit" isnt' really the defining thing that controls how drivers handle the road - many dense twisty urban environments are tight-enough to navigate that drivers instinctively take it slow and never even approach the speed limit. This tremendously reduces the odds of a fatality, although it does make minor scrapes pretty common.
You might be spot on - 7,500 kilometers per capita and year in Germany (2011) and 15,000 kilometers per capita and year in the USA (2013). This gives the same ratio as the road fatalities do.
I wouldn't be surprised if Germany is substantially more dangerous per-driving-kilometer than the USA, but with far fewer driving-kms per person.
Also, remember that in many locations the "speed limit" isnt' really the defining thing that controls how drivers handle the road - many dense twisty urban environments are tight-enough to navigate that drivers instinctively take it slow and never even approach the speed limit. This tremendously reduces the odds of a fatality, although it does make minor scrapes pretty common.