Wrestling your opponent down to the ground may well dominate in 1:1 cage match style competition, but that doesn't mean that it is the best martial art for dealing with every situation (like where the ground is covered with broken glass, or your opponent has a buddy or two who would like to kick you while you are down on the ground wrestling).
Now don't get me wrong. Nuff respect to Hoyce Gracie and all that. Brazilian Jujitsu is awesome stuff, but it is limited in some respects.