The 1-3 point IQ advantage is widely and consistently reported in the literature, and it's probably right as far as it goes. However, studies that additionally adjust for socioenvironmental factors (mothers who breastfeed are more likely to read to kids, have larger vocabularies, etc), show results around 1 IQ point:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1633786.
The "mothers should have the option" bit in the article was really off-putting. As if taking the option away was even on the table! It bears keeping in mind that the vast majority of the current adult generation was formula-fed. In 1971, only 25% of kids were breastfed in the hospital, and only 8% were still breastfeeding at 3 months.
As a metacomment, recommendations having to do with parenting are myopic. They lack any semblance of cost-benefit analysis, and the attitudes in the medical community about how women should mother date back to a time when womens' opportunity costs for labor-intensive parenting choices were nothing.
Also often ignored is how these choices affect fathers. Breastfeeding removes the father's ability to independently take care of an infant. Because feeding is a bonding experience, this creates a dynamic where the child looks at the mother as the last line in being comforted. This is a choice couples can make, but it is one that involves trade offs, which the medical community ignores. It would be one thing if they just left it to patients, neutrally presenting the data and letting parents evaluate the trade-offs. But they tend to hide the data and aggressively push their interpretation of the proper trade-offs.