That's Weta being weird and being wed to their PRMan pipeline using PantaRay as a first-stage radiosity solution which is fed to PRMan as an infinite series of

That's Weta being weird and being wed to their PRMan pipeline using PantaRay as a first-stage radiosity solution which is fed to PRMan as an infinite series of lights. It works, but from what I hear it's limiting their pipeline quite a bit. But then, they're Weta so they're more than capable of writing their own stuff and they're good at what they do :) ILM used to do something similar, but a lot of the big houses are moving from PRMan over to raytracers (specifically Arnold) with full GI support as it makes the overall pipeline and definitely artist look-dev a lot simpler and faster. PRMan 16 is also a very good raytracer now (it could previously do ray tracing through custom shaders).