why are online games are so addictive?

in south korea, a 28 years old man reportedly collapse and died after playing an online game for 50 hours straight.
by chemical reaction, Dr murni Wilson, director and senior consultant psychiatrist of the community Addiction Management program says, people may have a greater vulnerability to online games addiction. Advancing to the next stage of an online game gives them a buzz that makes them feel better and more motivated. This winning feeling is so rewarding that it's memory takes on a great intensity and becomes more desirable everytime it is recalled. The gamer may not win very often and reward may not come every time they play the game but they never know when they will win again or get reward.it could be the next hours, or the next minute, and if they don't continue playing, they fear they will miss the chance to win or receive rewards.
this article i take from reader's digest. publish in may 2007.