No, it is not rubbish. Please see here for the up-to-date WHO guidelines.
whqlibdoc.who.int/paho/2003/a85622.pdf?ua=1
"Breast milk can make a substantial contribution to the total nutrient intake of chil- dren between 6 and 24 months of age, particularly for protein and many of the vitamins. However, breast milk is relatively low in several minerals such as iron and zinc, even after accounting for bioavailability. At 9-11 months of age, for example, the proportion of the Recommended Nutrient Intake that needs to be supplied by complementary foods is 97% for iron, 86% for zinc, 81% for phosphorus, 76% for magnesium, 73% for sodium and 72% for calcium (Dewey, 2001)."
"...the Expert Consultation concluded that the potential health benefits of waiting until six months to introduce other foods outweigh any potential risks. After six months of age, however, it becomes increasingly difficult for breastfed infants to meet their nutrient needs from human milk alone (WHO/UNICEF, 1998)."
"Average iron intakes of breastfed infants in industrialized countries would fall well short of the recommended intake if iron-fortified products were not available (WHO/UNICEF, 1998)"
We are all aware that the iron in breastmilk has relatively high bioavailability; however, the amount that is in breastmilk to begin with is so small, that is it impossible for breastmilk along to meet a baby's iron needs once their iron stores are running low.
And it is not true that it is only premature babies who can become iron deficient; iron stores depend on a number of factors, and a smallish but statistically significant minority of infants are already slightly iron deficient as early as six months of age. See here, for example: online.liebertpub.com/doi/abs/10.1089/bfm.2007.0002