I think it would be different in different ethics. I would say the asian population is probably between B and C's.. The Caucasian and Latinos probably have a bigger average bra size, I would go for a C and D's.
You are largely right, since the average cup size is indeed B. However, the trend is in growing bra size (not unexpectedly), showing that it might not be long until the average bra size is C.
