I'm siding with Chilly on the majority of them have had something done. Implant, lifts, etc.
Also - changing hormones (obviously) can change your boobs (case in point I've gone from a B- to a D and am now dreading that I'll loose them!
); but did you know that liposuction can result in your boobs going up a cup size? They think its due to the estrogen/progestoren balance changing.
I hope that when Xtina finishes breast feeding that she replaces her bolt-ons, she can afford better tits than that!