Here is a brief blurb from the site:
The newborn gut and brain are only partially developed. Mother’s milk is needed to supply growth factors to close and differentiate the gut epithelium, and long chain omega-3 fatty acids for brain growth. Formula may eventually be supplemented with the needed fatty acids, but the growth factors/hormones present in mother’s milk will not be provided in formula. Recent studies have shown that hundreds of different genes are activated in gut cells from infants fed either breast milk or formula. Formula leaves the gut leaky and fails to stimulate the development of the immune system that is dependent on interaction with normal infant gut flora. These dysfunctions partially explain the increased (10X to 100X) gut and respiratory infections resulting from formula use. The reduced brain development with formula explains the five point reduction in IQ of formula fed infants.
You really need to visit Dr Art Ayers' website and read the full article for yourself.