That's not always true; small or moderate augmentation in the hands of a qualified plastic surgeon look and feel real.
The majority of porn starlets, however, aren't capable of doing research, going on consults with more than one doctor, and always go way, way, way too big. They also don't give themselves a month to recover. You're not supposed to be bouncing on cock for at least a month after surgery.
Case in point. Remember Melissa Lauren's boob job? Here's what happened to her doctor: