Basically a bunch of leftist Nazis operating in Germany, who have so much power in their hands that they can decide which video game can be sold to the millions of German gamers and which can't. After having recovered from the serious ass-kicking they got in World War II, the Germans are now basically on a crusade of penitence (especially after the school rampages occurred), shunning all things that are violent and bloody, more so than other countries - especially violent video games, doing all they can to protect their children from such "harmful exposure".
While they hated Jews, intellectuals, communists and liberals with Nazi-like fervor over 65 years ago, they now hate violence, blood and right-wingers with the same Nazi-like fervor.
Thus, the USK Nazis have banned (or mutilated) many awesome games from entering the German market in their original condition. Soldier of Fortune II, Gears of War, Gears of War 2, Mortal Kombat, Dead Rising and Left 4 Dead 2, just to name a few.
This leftist Nazism has had an impact overseas as well. Many US game manufacturers are aware of "the German problem" and thus ship specially altered versions of the games, where all the good stuff has been cut, to Germany, so that it may be sold there. Not only that, but the swastika flag in many world war 2 video games has been altered to look like a black cross - thus altering history. Looks like the Germans secretly want their precious symbology to not be shot at by american gamers after all, eh?
German dude: *sniff* you have no idea what the USK Nazis have done to us...we can't even play half the games you can!