I personally think the vehicles we use in the U.S. are way out of line with the speed limits we have.  Or maybe its the other way around -- the speed limits are way out of line with the vehicles we have here.  
Of course, it doesn't cost US folks $2000 and considerable training to get a drivers license like it apparently does in Germany.   We did that here and retail commerce would probably fall off.   
Practically any sedan you buy today, foreign or domestic, will drive/comfortably-cruise in to the 3 digits unless it has a limiter.  
All the German makes -- porsche, bmw, volkswagon, audi -- are built for autobahn driving.  Japanese  makes compete in most markets with the Germans makes, so the Japanese makes are often just as fast and as well-built.  And of course, the U.S. makes want to bring across the same build quality and performance as the German and Japanese makes -- and they've actually started to do that in the last 20 years with many models. 
If you took that Z4 and did 120mph/200kph in Germany, you'd just be "commuting to work"  Do that here and they have you sit in jail. I think it's all pretty silly.