I love this format. Let's not forget that the round robin format is seeded. The sixteen best players in the eyes of the seeding committee are placed in sixteen different groups, so those having a track record of excellence on the world stage are rewarded for it, just as it should be.
Nonetheless, pool is a sport in which the world's best hook up far too rarely for there to be a truly objective means of ranking and seeding all the players entered in the world championships. The round robin format says "if you can play some, prove it, and if you do, you'll get to compete for the world title." The real beauty of the round robin is that it enables every player in the field to showcase his talent and allows the pool fans of the world to learn so much about the players of the world.
I find this format extremely fair, and past results verify that the cream rises to the top. Some of the underdogs have now earned a right to run with the true thorougbreds of our sport, and in the next few days we'll learn who's got what it takes.
Making the knockout event double elimination would add several days to an already long event. I don't think it would be practical.