It has to do with isotope ratios. Xe has nine naturally occuring isotopes, with masses from 124, 126, 128, 129, 130, 131, 132, 134, and 136 Daltons. The ratio of these isotopes' occurence depends on the nuclear reactions going on in the star to form the Xe.
The different types have to do with the different chains of nuclear reactions leading to certain distributions of isotopes...
So, alternative lifestyle Xenon learns it from its parent nuclei. Remember this when other elements try to legalize unusual reaction pathways...
Bwahaha! Thanks dude... I blocked out all seventeen or so of my chem classes from my memory a long time ago... (Chem major in college. Gawd knows why. Hated everything but p-chem.)