QTR-Quadtone RIP

On a side note - does anyone have a graph of L* values that would appear linear to a standard observer? Looking quickly at the cyberhalides link and other references it seems strange that a perfectly linear response in ink density is desirable. Even though it is measured as linear wouldn't it not necessarily be perceived as linear because of the nature of standard human vision? What seems to make piezo curves so nice is that they appear linear, and in fact when measured and plotted are not perfectly straight; the slope increasing in the deep shadows to increase separation. Am I incorrect in thinking that human vision is not as good at separating dark values as compared to light and therefore an increase in slope at the shadow end of a curve would be required to produce a perceptively linear grayscale?