I don't get why TV manufacturers convert from RGB. Surely converting to S-Video or composite would increase their costs because it requires additional components? Isn't it cheaper to just use the RGB signal directly? Or are there technical reasons for not doing so?
There are technical and cost reasons: since you must allow those adjustments for composite and S-Video you have this function already implemented.
If you want to allow adjustment for RGB it has to be done for each signal (color component) seperately, thus requiring new hardware which will increas cost.
Since the TV (the components inside) can happily convert from composite to S-Video (to component) to RGB and back there is not much effort required to allow adjustments of RGB signals - just downconvert and upconvert.
Technically this is of course not the best way, thus a TV which does not allow adjustements for RGB should be purer or in case of TVs with RGB adjustments feeding a component signal can be better than actually using RGB.
Not all is as it seems ...
