Rather in the manner that I've yet to hear an electronic organ that sounds as rich as a real theater or cathedral one, I believe one of the biggest problems here is phase relationships.
With truly independent oscillators (pipes) there is none, what is more temperature changes etc. will cause them all to drift slightly differently. Capacitor charge and discharge variations will also cause them to trigger slightly differently, even (especially?) when the same oscillator is re-triggered.
Ultimately every note produced in a VST is related the the computers master clock, I can think of no way of avoiding that. Trying to synthesise independent variable drift would, I think, actually be a mammoth task.
It wasn't me!
(Well, actually, it probably was)