However they don't take several hours per frame otherwise it would take over 100 years.
It absolutely can take hours to render a single frame, and it doesn't take "100 years" to render a movie because they render lots of frames simultaneously. It's not like Pixar just has one PC in closet that does all of their rendering. Like the user above mentioned they have a "farm" of computers that splits up rendering jobs as they come in.
Unless they can get rasterized graphics to simulate light as good as ray tracing, ray tracing will eventually be implemented inside GPUs in the future. They have GPUs with 3,000 cores. If each core could perform calculations for ray tracing, you would have real time. Current GPU hardware limitations don't make that part so easy.
You seem to be rather mixed up about what ray tracing and rasterization really accomplish, as well as what's possible on current GPU's (here's a hint: people have been doing ray tracing on GPU's for years now).