I do have an iphone 4 and live in germany, too, and have not once experienced a dropped call, no matter how hard I actually tried to do the "death grip".
It is dependent on location, my experience is that in more urban areas the problems are more prominent, you probably live in some small city or a city with less providers or mobile phone users, or you haven't tried it in the bigger and denser located buildings. I can repeat the problems in the center of the city easily, but not so easy at my home. And it's not that I'm wasting time trying to repeat it -- it just happens if I hold it without the bumper case.
Once again: Death grip is the real "feature" of iPhone 4 when 3G is used. And it's the iPhone 4 problem, not the AT&T problem.
