Quote - What is clear to me is that in real life, there is no such thing as a light that only affects certain things (e.g. hair). If one cannot get the right effect from lighting that has global effect, that tells me that something else is wrong, and I'd much rather have that fixed than see lights that can be specified to only affect particular objects in the scene.

If you want to compare to real life, then you only have to look at studio photography where they also do selective lighting. Of course they cant get as precise control as in CG, but they use things like gobos/barndoors, bounce cards, light diffusers and precise control of intensity to make sure that light behaves exactly how they want it to.

As CG artists, we do much the same thing, only our tools are much more 'fake' so we compensate with equally 'fake' techniques.

Quote - I have no idea if they even exist in real ray tracers, like Mental Ray or vRay.

mentalray has them, as well as deep shadows (called volumic shadows in it) Dont know about VRay.