As far as I understand, gamma-correction is applied to adjust high range of luminance in real world to relatively low range of luminance in displays.
And if it's goal is to adjust luminance, why it is applied to all of the RGB channels independently?

In most popular color models which include luminocity (like YUV) the luminocity term itself is computed with different coefficients for RGB channels. So why gamma coefficient is the same for all RGB colors? And why it would not be logical to apply this coefficient to luminocity term only and remain color space untouched (UV terms in case of YUV model)?

Is this connected somehow with the fact that there are three types of cones in human eye which more or less correspond to RGB colors?
But even if cone cells adapt independently from each other, the light intensity for all of them should be uniformly adjusted by the work of lens and pupil.