IMO it is all about the cannabinoid receptors in our nervous system. If you are at a saturation point where nearly all of a body's given receptors have received their signal. There must be a point of diminishing returns. This would be subjective according to each individual's own nervous system. This may be the point where the entourage effects of the other compounds present in a strain produce the various different effects, thus the different "feelings" from different strains.