Lag doesn't happen in every game, but it does occur. Because of the way the networking code is handled, one person with a lousy connection can force the lag onto everyone else. Or one player with a very weak computer can cause the game's speed to be throttled to a crawl. The problem is that in many circumstances, you don't know that you'll get into a laggy game because, even with a great ping, an individual could still have a weak computer or meh internet connection.
So, if you are having lag free games, then that's great, but I trust you'll eventually bump into a laggy game. By and large, I hit the occassional laggy game, but its generally not too bad... maybe 2 out of 10 games will be laggy and 1 out of 15 will be unplayable due to lag.
