Gee Nat! You are logical but my own observations of the human condition offers the fact that logic does not explain much.
I listen a lot and what I hear from women all over the world is a little bit different (however those with problems are more likely to complain) - however there are also surveys.
You cannot lump all women together, breasts vary enormously in shape, size and texture and evolve over time - women are not like cows!
I think we have to distinguish between 'support' as you put it, and discomfort. here is no good evidence to suggest breasts need supporting - I agree. But it can get darned uncomfortable for some when 40Gs start bouncing hard.
In a forum like this we have to support (pun intended) the individual girl or woman.