There are most certainy writers involved in reality series and a lot of that also gets edited in certain ways to make things look how they want it to.
But it's not all fake. I mean in the Big Brother house they are filmed 24/7 and you can watch the live feeds. So it's basically completely legit, but when they talk to the camera in the diary room, it's quite obvious they are being fed lines as well as during the games and events.
From my limited understanding of The Jersey Shore due to my friendship, a lot of that is also legit, but the producers certainly stir the pot and also will edit things to make it look a certain way.
Of course when the cameras are always there and filming, obviously a lot of it isn't going to be truly genuine though, so even if it's not scripted, a lot of reality TV is going to look stupid. But I think that's why I like some of it, I for some reason lately have enjoyed watching real people look stupid on TV. (and no, I'm not talking about our politicians)