Oh come on. With all due respect to the German techno pioneers (all the guys you mentioned + Torsten Fenslau, Oliver Lieb, the Voight brothers, Thomas Fehlmann, Ernestus/Von Oswald, etc.) and to all the kraut/avant/early electronic guys who came before them, that's just not true. As I suspect most of those German techno pioneers would be the first to admit.
This, for example. Not to say that Detroit was the sole birthplace or that it produces the only true/pure/etc. techno, rather that Detroit & Germany were heavily influential on one another. And still are - just look at Moodymann/Parrish/Omar-S etc. and the recent surge of Euro deep house.