The top flippers with the lightning bolt are slightly smaller in length, and were installed after the designers found the games "too easy" - thus increasing the chances of a ball going SDTM (straight down the middle).
This isn't quite correct. They were introduced at the request of the European distributors, who were getting feedback from operators that wanted less ball time per game. They thought this would lead to greater income per machine. Mark Ritchie explains this in his TOPcast interview.
