It's quite an interesting point you make, i certainly always thought that the older footballs were heavier, although it appears not to be the case. Footballs were originally 13-15oz that changed to 14-16oz, so not really any difference, so why did the older footballs appear heavier and more cumbersome. It appears it was down more to the raw materials that were used in the early days, and the dangers of heading a stitiched ball! Although there was some weight difference dependent on weather conditions, today a ball is not allowed to weigh more than 16oz including water absorption, whereas older balls held a lot of water and i don't think there was any regulation governing this. I think it's more the aero dynamics of footballs have improved rather than the weight, due to the changes in material and the manufactoring methods now used.
I agree the weight of footballs over the years have not necessarily changed. It's the materials. The leather in the old balls were stiff and hard, whereas modern balls have so much cushioning to make them softer.
My Barney destroyed a football of my sons recently and I could not believe how much material they use inside the ball!
