Their are differnt set-ups that feel differnt on the track, as every drive likes to drive a little differnt then the guy next to you. So if one persons set-up is night and day differnt then yours, but you are still working on driving a little better, keep in mind your set-up might be just as fast as the other guys or it could be even faster then his once you learn to push the car a little harder. It might be tempting to switch to their set-up but that might hurt you in the long run, as being that every one likes their cars to feel a certain way.
I for one tend to like my car to rotate through the turns, but have a nice rear end grip feel with maybe a light push (for off-road), while the guy next to me might have the same car they might like the rear end on the free end with a car that cuts through the turns. The bigest thing is as long as you can drive consistency around the track with some fast lap times, and you like the over all feel of the car then that might be the set-up that you want to run eventhough the other guy might be running a differnt set-up.
Also sometimes it is just that that other guy found a line around the track that might save a few tenths in some turns and that is why they are pulling away from you, not because their set-up is differnt.
(wo that was a lot of typing for me, lol)