You don't have to believe in a everyone-is-a-special-snowflake theory of human nature to acknowledge the following observations:
a) human morphology roughly adheres to a normal distribution along most dimensions (height, weight, length of limb, circumference of torso, etc.)
b) normal distributions have outliers
Economies of scale in (inter alia) textile production mean that making, say, men's trousers inside the 95% interval for waist/leg size combinations will be cheaper for manufacturers. They don't have to cut new patterns or rig up new workstations or anything. They just crank out the same ol', same ol' again and again. Ditto automobile bucket seats, ditto kitchen counters, ditto pork pie hats. Ditto just about anything where the product interfaces with the human body.
I might find a more eloquent or subtle way of saying this, but I elect not too. Boobs are getting bigger. The mean bra size has gone from 34B to 34DD over the past couple decades. And it's come to my attention lately that some of my more ample female friends have a difficult time shopping for well-fitted, attractive brassieres in many of the more common retail outlets. And when they do find one that fits and doesn't look like a replica costume piece from Zardoz, they often pay out the nose for the garment. I cannot imagine the circumstances that would lead me to pay fifty bucks for a pair of drawers.
So, how about it? Are ladies who clock in north of a double-D being exploited? Good old price theory would say "probably not": if there has been a shift in the distribution of breast size, a natural arbitrage opportunity has arisen, meaning that entrepreneurs should be able to fill in the lacuna in demand (this holds for changes in both the first and second statistical moments). If that's not happening, there are some frictions in the market.
And it's possible that EE can help point us to one important friction: substitution. If busty women simply buy brassieres less frequently, taking greater care of them, or wearing them a bit past the point of destruction, this will mask a right-tail boob size increase. Slow sales are slow sales, whether it's because of consumer behavior or because of underlying demand characteristics.
So what's the remedy? In this case, it's difficult to tell from a distance whether or not there are other barriers to entrepreneurship (like challenges in the design or manufacturing process) that immutably contribute to production costs, but busty women and the companies they frequent owe it to each other (remember, this is a reciprocal arrangement) to communicate better. Bra markets would be more efficient if large-breasted women would be more vocal about their challenges in finding the products they seek. A decent PR firm should be able to make a few bucks off this. Bug in your ears, y'all.