Nutrition aside, there are two reasons I felt it was important for me to breast feed my son -- allergies and TMJ. I have a terrible time with both of those (I was bottle fed, because my mom says she was too self-conscious to nurse, which she now deems a lousy reason not to bf) and studies have shown that nursing can reduce the likelihood of allergies, and nursing at least 6 months can reduce the risk of TMJ problems. My ds is 16, has milder allergies than I do, and a limited amount of jaw popping, nothing like what I dealt with since I was very young.
It wasn't until after I had my son that a study came out showing that there are cardiovascular benefits to breastfeeding. I know someone with a son close in age to my son who didn't breastfeed, and although I never mentioned that study to her (it would have done no good, it was years later) I always wondered if her son's high cholesterol (from very young, before I knew him, when he was 4) might have been in part caused by bottle feeding. (The cholesterol making mechanism will turn on if there isn't enough cholesterol in the diet, because the brain needs that to myelinate the neurons.)
At a guess, Jennifer Lopez made up her mind, then searched for information that would support her decision, not searched for information and then made a decision.
There are valid reasons not to breastfeed -- illness that could be passed to the baby, or that would make it too hard on the mother, inadequate supply (though that can't be determined until after trying!) I haven't heard of those being a factor, though.