For a school gifted program, I would expect there to be an appeals system in place to handle "near miss" kids, as well as multiple possible points of entry. (For DYS, you can obviously enter at any time, so you could take the SAT again at the next administration or the WISC again after 2 years.) Basically, for something that is going to have a significant impact on education for a child's life, there should be a way to deal with a single bad test day so that they are not excluded.
For a random one-off opportunity (say, a camp or an extracurricular class), I would expect relatively rigid adherence to a rule with no appeals process, because the cost of excluding someone who "ought" to be eligible is low. Almost no one has their life changed by one week at camp.