You do not have to have hip scores and eye tests to show your dog, you need to have them done if you are going to breed from your dog, or if you have the breeds interests at heart.
All dogs need to be healthy, therefore you need the parents of the dog to be tested and proven healthy (to be tested, and the tests recorded officially they have to be registered with the KC). When the puppies are born most breeders register the litter with the KC, this encourages people who go on to breed from the pups to have them tested before they are bred from.
Anyone can register with the DL club and it is not worth the paper it is written on. What does it prove? Why bother?
A KC registration means that you can trace your dogs pedigree going back generations, you can find out information about your dogs parents, grand parents etc. and can even get photographs of them if you so desire.