You are right. It's not really universal. I should have thought it out more. Weight and build of the body needs to be distributed over the bike equally to get maximum comfort and efficiency. There are factors that need to be counted in...Type of riding... Strength of upper and lower body (which is subject to change). Arm length... Age,,Etc. However, more often than not you'll find it to be the case because of physics that are involved with striking that balance when it comes to those types of bodies.

I have relatively long torso compared to my legs and since I do my own fitting, I did experiment a lot with being more forward. Anytime I did, I would initially be faster, but after some time my body would get beat up fairly badly... I would feel pain in my back, knees, shoulders and I would sit more on sensitive areas because the weight of my upper body would tilt me forward naturally, which would also force my back to be more bent.

With me being more to the back, it's so much more comfortable and I've been noticing that there is some kind of supportive connect between my upper an lower body when pedaling in a way that I use the weight or maybe even muscles from my upper body to make pedaling more efficient somehow.

I would imagine that the opposite would most likely be relatively true with long legs and a short torso in most cases.