Well that is because the Abitur (german high-school diploma) is regarded equally no matter which school you attended. From what I gathered the US high school diploma is worth pretty much nothing, without knowing somewhing about the school and/or a high amout of AP-classes. Compared to the German degrees, I'd argue that its actually closer to Realschule (the 10yr grade, which does not qualify for university), than abitur. (Except you are at a top-notch school and take lots of AP-classes)...