Unless I am missing something as well, don't think you are missing anything. Don't even need to get the component mask for R in your one> You are component masking a float but it's already a masked float straight from the vert color node, so that shouldn't do anything. The other graph basically ends up multiplying the vert…
Ah, so It allows to have up to 8 textures to mix together using vertex color and alpha. A bit of an offtopic, but first thought I had after reading a title is split UVs of vertex color/alpha to have rough transition between values. Not sure it even makes sense with other software or file formats, but 3dsmax allows for some…