Psionatrixes and their Affinities

[Xaendreth]

In the EPH, there are listed psionic items called psionatrix that are reference in the Complete Psionic as the base items. In the CP, they also list stacked psionatrixes and each one listed says they are have affinity to one of the schools of psionics. What is the purpose of the affinity?

[Tzardok]

On first readthrough I thought that you could stack a psionatrix only on a base psionatrix to which it has an affinity, but then I saw that this is explicitely not the case. So I've got no idea after all; it seems completely meaningless.