Some sports are ridiculously expensive. I could understand why they may want to concern themselves if they were paying 1-5k/yr. Now imagine doing that for 10-15 years.
As well, I often see scores of parents chiming in that they believe there is a value in what they pay for their children over on chalkbucket.com. (a gymnastics forum) Their kid may never hit the optional levels much less be an elite, but there still is something to be gained by them participating in said sport, whatever sport it is.
As a parent or coach, I would never tell the child the results of the test.
I saw Dr. G originally post this and found it pretty interesting. Even more so than the lack of myostatin gene in some children and animals.
However, more so than just the potential, there lies in the mentality of the athlete. We always here how so and so has so much potential, but never amounts to much or fizzles out (gets bored), etc. Quite often in many sports, it's who sticks around.
Looks like she'll never be a good marathon runner, though.