The ATX plug is your usual 24/20 pin affair, with the main plug itself using the clip system adopted by many to give you the choice of 20 or 24. Why still use 20 pin, well the main reason is that it's still required and until it is not I don't see these clips changing at all. I would still like to see a manufacture use there initiative one day as most motherboards have the connector on the right side of the motherboards edge and I believe that the main connector on PSU's could be an L bend type which would be more practical.