I thought local burial practice were dictated by the soil type and availability of someone to actually 'bury' said corpse. The whole "exposing the corpse to be picked clean" is reminiscent of Hindu and MesoAmerican practices that I have read about..I could be wrong though :S
"The Universe is run by the complex interweaving of three elements: energy, matter, and enlightened self-interest." G'Kar-B5