WoW has actually toned down the Skinner box effect. People would get stuck trying to repeat an event 10 times with a 20% success rate per try. If you have a lot of players then the number of people screwed over by getting the long statistical tail resembles the participant count of your forums. Bad press.

So you get credit for effort. Your odds go up with each attempt until you succeed. Rare items though, still Skinner boxes.