Well for one pixar dont do humans or hyperreal stuff. They do stylised work where character and animation are given priority over making things look photoreal. That way they are able to get away with lots of cheats since the viewer expects a toonish look in the first place. Plus PRMan didnt even have raytracing till a few years back so its not as if they had the option to use raytracing.

Also to add to Keith's post, in animation renders the single most important point with lighting/shadows is consistency. ie your lighting quality should not change from frame to frame. If you can manage this, the human eye will just outright ignore any defects in the lighting itself (as the viewer would be too busy looking at the motion instead) Of course you do need a minimum level of quality, but the level is much lower then say if you were doing a still render of people or architecture, where the eye would be free to roam around and pick at various issues. And of course moblur also hides a lot of artifacts.