The censoring of the Nazi symbols is a direct result of WWII. There's a lot of symbols banned, actually.
Here are some (all except the last two are banned). The censoring of all the blood and gore in games takes place for one sole reason: Sales. See, if you can't advertise a game with lots of more or less unnecessary violence, you'll lose a lot of money, because Germany is a big market. So what they do in order to be allowed to advertise the games is, they censor them. Red Blood is turned green or removed alltogether, corpses just fall over and disappear instead of bleeding out and lying around waiting to be shot over and over again and so on... Of course, this takes away a lot of the fun playing, since you have this nagging feeling in the back of your head that you haven't seen it all. That's why clever people invented a thing called "Bloodpatch". Bloodpatches just turn off the censoring and you can enjoy the game in all its goriness. Or if you're not willing to wait for bloodpatches, you simply import games from somewhere (preferrably Switzerland, because of the shipping cost) and you get an uncensored version.