There are many factors involved in determining ear strength, shape, carriage, etc. From what I've read, at least 27 different genes are involved in determining characteristics of ears. A few characteristics that determine ears include:
How wide or narrow the ears are set on the head
How tall the ears are
How wide the ears are
Thickness and heaviness of cartilage
Degree of curvature of the ear
Problems such as ear infections
Muscles of the jaw are also involved in the developmental process by which ears strengthen and rise on a GSD puppy. When a puppy chews he is also strengthening muscles that affect the ears as well as the jaws. Puppy ears normally go up and down and as a rule, if the ears are consistently at least halfway standing by 6 months of age, the ears will be all the way up by the time the dog is a year old although ideally most breeders prefer puppies ears to stand much earlier. More harm than good though, can come from botched attempts to tape or prop puppy ears.
The German shepherd dog in the show ring is a movement breed and as long as a dog's ears stand when the dog is posed and alert, little attention is given by the judge to ears.