I've enjoyed beer in both German taverns and Scottish pubs; never once was I served a warm beer - the most warm was a mid 50ish degree bitter in Scotland. My old man, who was stationed in Germany, has said on multiple occasions that beer in Germany is served at BODY temperature - when I tell him that it means that the beer is nearly 100 degrees, he quickly restates room temperature (not cellar temperature).
My feeling from hearing this so many times is that it's essentially an urban legend that's come from folks either misunderstanding or misstating (i.e. body temp) something with which they don't necessarily have a lot of experience. Subsequently, people who hear these things "learn" misinformation and then propagate it by citing the faulty source.