A few thoughts on the subject.
First of all. Breasts are not just for feeding infants. I am an avid supporter of breastfeeding, but, I don't kid myself about the nature and purpose of breasts. Breasts are partly sexual in nature, part of our dance of mate selection. The size and nature of human breasts is fairly unique in the animal kingdom... we have way more breast than is required to feed a child, and they never really go away once the kid's done needing them. To say that's all they're for is a bit of a lie. They are also sexual in nature. Like it or not.
Second of all. Nursing is partly a cultural concern. Different cultures have different guidelines, set according to cultural values. Because our children are often done staying at home with us by the age of 4, we start teaching them about privacy of the body at a fairly young age, and modesty is something our culture instills at a much younger age than others. Thus, nursing until 4 in other countries is only relevant if they have the same standards of modesty and parental attachment at said age.
Third. The most damaging thing you can do for your child's emotional development is to make them 'weird' in the eyes of their peers. This mother has ensured that. Whatever parenting attachment benefits there are, that'll outweigh it for sure.
Fourth. I nursed later than is socially conventional. I nursed my daughter straight through from her birth until she was about 2 years old. In that time I got pregnant again and had my son. I nursed both in tandem for months, and only quit with my son when medical issues completely unrelated made me have to quit due to medication. BUT. I acknowledged cultural norms by making it clear after about 18 mnths old that my daughter was not to nurse in public. She knew it was a quiet, at home, comfort thing.