I race on a closed private server, consisting of friends - which admittedly makes "my" server a bit different. However, there is no doubt that when two drivers enter a corner (say, after the back straight on BW) the "inside" driver is often the guy who is trying to gain the position, and it is considered very bad "sportsmanship" for him to take advantage of his line to the point where he runs the other guy off.
If I'm on the inside thru' a turn, and we're both on even terms, I'm going to leave room for my opponent on the outside when coming out of the turn, unless I am absolutely sure that he's not there - and that hardly ever happens.
We all love racing, and noone wants to win by causing an accident. Everyone leaves room for eachother, because there's no fun - or bragging rights - when you ruin an awesome race for eachother. I'd rather have a door-to-door fight over several laps, and finish second, than just take the easy option, and win without being the better driver.