I think you are missing a shift that has happened in the industry over the last few years. Yes, now that computers are fast enough, pixar raytraces everything in renderman. Most other major studios use that or arnold, a pure raytracer.

That's Pixar - they're behind the curve, and PRMan 17 and 18 (their commercial renderer they sell) has been pretty poor at full raytracing (monte-carlo integration) due to poor acceleration structures and the overhead of their RSL shading language.

PRMan 19 looks like it's going to fix these issues to some degree.

Other renderers like Arnold and VRay (full raytracers) have been being used for the last 5 years by other studios.

You are absolutely right. People should stop upvoting my post because I'm totally wrong. Not only was Cars the first movie that was done using ray tracing, they thought it was glitchy and MU which was released 6 years later was actually the first movie to be fully raytraced.

That said, the technique they did use was scanline rendering, which is still rather different from z-buffering, which is the way GPU's generally render.

Of course now I'll change my argument that Pixar is after a non-realistic cartoony feel, so that gives them more freedom.

If you look at live action movies, the CG parts in there are either painted or ray traced, they need absolute control to be able to blend them.