I'm trying to think of girls who were naturally blessed that entered the industry a bit on the chunky side and then slimmed down... I think it's a good trade for a very busty girl to go down a cup size or two if it gets her a flat stomach and a slimmer waist that contrasts better with her hips. The kind of change from needing to wear something around her waist during the whole scene, to instead she can strip naked during the tease and the camera lingers on her midsection and you find yourself mumbling "wow".
Amy Reid is one example, but not a good one -- she already had a great waist before she lost weight (very healthy looking girl) -- she lost a cup size in exchange for a leaner (looks better on camera) face... which isn't as good of a trade in my book.