A couple of thoughts:
-The talent search programs tend to be very similar for the rather straightforward reason that most of them were founded by professors from the same academic lineage, generally with roots in Julian Stanley's research group at JHU and his collaborators.
-The history of the searches includes innovators whose contributions were motivated by the frustrations of highly-resourced parents who still could not find good educational solutions for their children (in some cases, early researchers involved their actual own children, deidentified, of course), as well as innovators who wondered why reports of EG/PG learners were so much more rare anecodotally than psychometrics would have predicted, and set out to lower the bar to identifying them in a psychometrically rigorous way.
Either way, they began from university research labs and worked their way out to larger swathes of the population. It seems that many of the resulting programs have retained a higher value for statistical rigor (thus controlling for variables, such as the type of test taken) than for the types of integrated, multi-factorial admissions approaches current among the majority of application-only institutions at every level of education.
There is value in both approaches to selection, especially at an institution such as SET (and others), which continues with ongoing research on the eligible pool. (They are, after all, the --Study-- of Exceptional Talent.) Changing their qualification criteria might, in their view, jeopardize some of their long-term research, as comparisons across pools would become much more challenging, if not impossible. The re-centering and re-designs of the SAT have already thrown some dust in that air.
CTY, in contrast, is an educational entity whose mission is much more about meeting the intellectual and social needs of the students who participate. Consequently, its leadership likely feels more freedom to explore/apply more generous (and accessible) criteria. The current pilot study to use routine school-administered instruments for eligibility purposes suggests that equity and access is something they are attempting to address.
