In my experience, driving on US freeways requires less lane changes than on German autobahns. This is mostly due to the facts that in the US everybody is driving about the same speed; in Germany, as mentioned above, if you want to drive faster than the trucks but not fast enough to stay always left, you are constantly switching lanes to overtake people in the second lane. If you want to drive a speed that is lower than the 'general' second lane speed, you even need to go in and out from the truck-lane.
Furthermore, since it is OK to overtake on the right in the US you don't need to change lanes if your lane now goes a little faster than the lane on the left. Even though you shouldn't stay left for a prolonged time if you are [much] slower than the rest (even in the US), it is OK to be overtaken on the right.
Though, I am faster on German freeways (driving around 160-170km/h), I enjoy driving in the US more as it is generally more relaxed.
I somewhat doubt that the German autobahn rules are better with dealing with medium-high-traffic situations than US rules. Would be interesting to see actual data on this claim.
The relationship between forgiving roads and safety does not necessarily run in the direction you assume. People generally drive at a speed that feels safe, so a road that feels safe will have faster speeds. Faster speeds don't necessarily lead to more crashes, but they definitely lead to a higher rate of serious injuries and fatalities.
Given a difference in fatality rate between two developed countries, I'd definitely look at factors like traffic engineering before jumping to the conclusion that, say, Americans are just worse drivers than Germans.