For amateur and pro poker players alike, if they can travel to one poker series a year, it's generally going to be the World Series of Poker.
Pro players plan their annual schedules around the WSOP; amateurs save up for their yearly Las Vegas binges and everyone has become used to things being done and set up a certain way at poker's biggest gathering.
However, each year, there are small changes to the event as organizers strive to improve the WSOP, sometimes in response to player feedback and other times simply because they think they've spotted an inefficiency that can be corrected.