I know nothing about how a simulator is made, but as a heavy user I realize some things that are different in LFS facing the others.
One thing that for me differs LFS, is "to be inside" of the game.
RBR, RF (and its mods such Simbins games) and NKP look like I am sat within a simulator cabin, with a screen in front of me rolling the track, in the same manner of those malls "simulators".
I could say that there are two enviroments in those games, one is the cabin, other is the world outside that you see on the screen.
That is so evident that if you change the camera from inner to outer one, you notice that the things change in something. You loose the contact.
I'm not saying anything about the physics. It is just that feel of "to be inside".
LFS is different. It gives the sensation that I'm "in" the game. Everything happens in one unique environment, your car and the track are in the same virtual space, and you are there.
So when you change your point of view (from the inner camera to outer camera, or from your car to the others cars), the "things" are still there, the same 3d models, the same environment, the same textures, the same everything.
Things don't change when you change your camera, cause there are no tricks, there are no virtual inside the virtual, there are no lies, everything in that little virtual world is true in some form.
This manner of doing the thing is probably the best element of the fantastic immersion that LFS gives.
The other thing and this is as so important as, is the Force Feedback. The FFB of LFS has no effects trying to imitate something real. It only reacts to the forces that act on the tyres and suspension arms, nothing more than that.
That feels real, that is sincere, that gives immersion.
The physics of LFS is not an accurated model of the reality, but it is related with its own world. And it is fiel to itself.
I use to say that LFS is not a car simulator, but a racing game with a virtual environment that imitates cars and tracks.
It has its own world with its own physics, and you feel it cause you are inside the game.
As I always say and it is on my signature: LFSensation, you know when you feel.