First off....
I didn't mean to imply that adoptive parents and children do not have a bond! And I do have to point out a flaw in expat's comments about bonding...just because they are your biological children does not mean you naturally have a bond. It is a choice, even if you are not aware of making it.
VNP was right...bonding is very important for psychological and physical wellbeing...the studies are well-known and I don't need to get into that. And, I don't think she was saying that bottle-feeding moms and/or dads can't bond with their children. Bonding, feelings of well-being and "belonging" can be nurtured by skin to skin contact, warmth, nourishment, eye contact etc...all things breastfeeding provides. You cannot put a baby in his/her stroller and prop up a bottle...the mother and infant are in close physical contact. Hormones make it a pleasant experience for the mother. It is a mutually satisfying relationship. Newborn's eyes focus at about 10-12 inches, which means that when he/she is breastfeeding they can see their mother's face clearly. Did you know there are studies that show that newborns can smell which mom is their own?
But, I am not really talking about breastfeeding your own baby...I was trying to say that breastfeeding is beneficial for an adoptive baby because it gives lots of skin on skin contact, associated with nourishment and contentment, and that helps the parent feel like this child is really theirs and help the child feel like they belong to the adult. I am NOT saying this does not happen with bottle-fed children at all....I am just saying that breastfeeding is a wonderful way to establish a relationship with an adoptive child.