In the post "What is Saturation? And How to Get Optimal Saturation" it is state that "Colors also have a greater potential for saturation when they have an imbalanced ratio of red, green, and blue. This is because RGB values that are closer to one another are more and more grey, such as the (128, 128, 128) example from earlier, which is middle grey. The saturation slider would have to be increased to impossible levels for (129, 128, 128) to appear as very saturated red."
It is not clear to me why one needs imposssible levels for saturation to obtain (129, 128, 128). Using Color Picker in Photoshop I obtain HSB (0, 1, 51) which is very low saturation as you claim, not an impossible value.