I guess even though it isn't actually reality, how everyone reacts to the situation is. There are no scripts, that we know of, so what happens and how everyone reacts is how a real person would react, that is as far as they're concerned at least.
So to sum it up, they are real people dealing with not so real situations. But they do have real feelings and real thoughts and they are real pains in the ass. When put together, reality tv is born.