I do have to ask, is it more a bond that the mom develops with the child? Because I don't know if a child understands the difference between nursing and bottle feeding. Or are we saying those that don't nurse, don't have as strong of a bond with their kids as those that do, throw in along the lines that fathers will not be able to bond as well with their kids.
I've read studies that breast fed kids are supposed to be smarter than bottle fed kids. That nursed kids feel more secure throughout life and closer to their parents (when it should just be mom) than bottle fed. While I support nursing, I think there is a segment that ends up trashing moms that can't/don't nurse.
For sure there is a bond that happens on the baby's end of nursing. Comfort nursing is a big thing with children, as is reverse cycling.
My eldest was very utilitarian about nursing. She ate when she was hungry until she was full, then was done with it. My youngest wouldn't eat during the day by bottle, so he'd be up all night nursing - this was from a young age. He comfort nursed from the day he was born, just to cuddle. He's still much more of a cuddler - he's our puppy, our daughter is a cat.
While there is a unique bond that happens with nursing than with bottle feeding, different doesn't mean better. Eye contact, cuddling, and so on are integral to the process of both in order to get the bond. I think part of what makes that mother/child bond specific in nursing is that nobody else can do that besides mom, so there's a ton of time together - if you're the only person bottle-feeding your child, I'd gather it's similar.
In addition to what cowgirl said. There are supposedly certain enzymes that help brain growth in breast milk, and things that promote antibodies. However, breast milk is low in vitamin D, while formula is not. There are certain things unique to each.
I think it's sad when people trash moms who can't or don't nurse. Just like it's sh**ty that people trash nursing moms in public or at work, or back in the 70s and 80s when it wasn't in fashion. As long as your kid is fed, how is nobody else's business. Just like circumcision, people are WAY too up in your **** about this from birth.