I tend to agree - unless you had the ability to compare the ride of identical frames made of different materials - same angles, same components and tires, I suspect a lot of the 'feel' of the ride comes from having been told steel is more forgiving, aluminum is harsh, etc. We have a lot of very subtle control over the frame, angles, wall thicknesses, and I would expect a skilled builder to be able to produce the desired performance for whatever frame material. That said, there do seem to be some obvious poor choices, I am not going touring on an all-carbon frame that could fail catastrophically in the middle of nowhere, no matter how comfy.